While it might be said that many of the Centaur mystery man characters belong in the same universe there are a number that probably don't. These are future/science fiction series characters of which the Iron Skull and Satan Rex were the two longest running.

A word about the Iron Skull series. It takes place in the 1970's after a very long and devastating war. Interestingly, this second world war seems to have taken place decades after the WWII of our own universe.

Air-Sub DX - This was an experimental aerial/aquatic vehicle.
First Appearance: Amazing Mystery Funnies #7 (Mar. 1939).

Avison, Al - Avison was the head of the Purple Dragon Gang. He fought the Iron Skull in the 1970's.
First Appearance: Amazing-Man Comics #16 (Oct 1940).

Baron - Aided by his servent, Llasco, the Baron was building an army of robots in his secret mountain lair. Using a magnetic transporter beam, he captured the Iron Skull to use his blood to animate his robots. He was defeated by the Iron Skull.
First Appearance: Amazing Man Comics #15 (Aug. 1940).

Burke, Timothy "Bulldog", Lt. - A police/intelligence(?) officer associated with Dr. Jon Linton in his fight against Satan Rex.
First Appearance: Amazing Mystery Funnies #15 (V2#11, Nov. 1939).

Cult, Devil's - This is criminal organization fanatically loyal to Drago.
First Appearance: Amazing Man Comics #11 (Apr. 1940).

Decor - When the Skull and his gang had faced several crushing defeats they hired Decor and supplied him with with several  powered battle suits. With these he formed a gang. They were defeated once by the Iron Skull in the 1970's.
First Appearance: Amazing Man Comics #6 (Oct. 1939)

Drago - A scientist slaver Drago was the head of the Devil's Cult. Despite his robots and advance scientific devices he was captured by the Iron Skull then shot by his pan-asian employer to prevent him from talking.
First Appearance: Amazing-Man Comics #11 (Apr 1940).

Dryak - This is a six-legged, horned, dragon-like creature inhabiting Mercury.
First Appearance: Amazing Mystery Funnies #19 (Apr 1940).

Gang, Purple Dragon - This gang was part of the Yakuza, a world-wide criminal organization that dominated much of the world's crime in the 1970's. One on its most notorious heads was Al Avison.
First Appearance: Amazing-Man Comics #16 (Oct 1940).

Hasting, Dan, Lt. - Former rocket pilot for the United States of America's Division of Aviation. Now he is a lieutenant with the Aero Inter-Stellar Guards.
First Appearance: Star Comics #1 (Feb 1937).

Iron Skull - In 1970, during the Second World War, Dr. Watson found an american soldier who was near death from his battle injuries. He operated on that unknown soldier and transformed him into the cyborg known as the Iron Skull. Although he was unable to remember his past he chose to use his new super-human abilities to oppose the criminals and mystery villains who would prey on the innocent during the post-war recovery. His most noticeable feature is his missing nose, which is what earned him the name of the Iron Skull.
First Appearance: Amazing Man Comics #5 (Sep 1939).

Kane, Damron, Dr. - This is the head of a secret government research base. Though a brilliant scientist in his own right he has voluntarily turned over directorship of scientific activities to Dr. Jon Linton while retaining administrative control and his own research. He is the father of Dr. Lisa Kane.
First Appearance: Amazing Mystery Funnies #15 (V2 #11, Nov. 1939).

Kane, Lisa, Dr. - This is one of the scientists working at a secret government research base in Alaska. She is the daughter of Dr. Damron Kane and the girlfriend of Dr. Jon Linton.
First Appearance: Amazing Mystery Funnies #15 (V2 #11, Nov. 1939).

Kodi, Menna, Lt. - This is a member of Space. Her partner is Nicki Nelson.
First Appearance: Amazing Mystery Funnies #19 (Apr 1940).

Kosterman, Owen - A space pirate encountered by Nicki Nelson and Kodi.
First Appearance: Amazing Mystery Funnies #16 (Dec 1939).

Lak, Dahl - This tibetan monk was the servant of King Satan for many years in the City of Mists in Tibet. He finally left the city in time to alert Jon Linton to Satan Rex's plans to destroy the Earth who stopped them.
First Appearance: Amazing Mystery Funnies #15 (V2 #11, Nov. 1939).

Lemerise, Charles "Chuck" - This was one of Al Avison's top Purple Dragon gangsters. He remained a Purple Dragon for most of his adult life. He fought against the Iron Skull several times. He is an inhabitant of the Galaxy 2100 universe.
First Appearance: Amazing Man Comics #17 (Nov. 1940) - There may well be an earlier appearance.

Linton, Jon, Dr. - This brilliant scientist is the technical director of a secret military base in an inactive volcano in Alaska. In this base he has managed to build a number of incredibly advanced devices including several nuclear reactors. At one point, Satan Rex sent the Sons of the Atom after Linton because Linton’s knowledge and abilities might make him a danger to Satan Rex’s plan to take over the Earth. Since then, Linton has taken the fight to Satan Rex.
First Appearance: Amazing Mystery Funnies #15 (V2 #11, Nov. 1939).

Magno, Dr. - This was a mystery criminal with magnetic powers that the Iron Skull fought in the 1970's.
First Appearance: Amazing-Man Comics #8 (Dec 1939).

Man, Balloon - This is one of the intelligent races inhabiting Jupiter. They can inflate their bodies with gasses that allow them to fly through Jupiter's thick atmosphere. This allowed them to dominate other races whose weapons could not reach them. When first contacted by the Space Patrol they proved extremely aggressive but they were little match against opponents who could fly faster and higher than themselves.
First Appearance: Amazing Mystery Funnies #21 (Jun 1940).

Man, Mole- - This is an intelligent humanoid mole being inhabiting Mercury.
First Appearance: Amazing Mystery Funnies #19 (Apr 1940).

Man, Spider- - This is a low-intelligence humanoid spider being inhabiting Venus. They are cannibalistic and will eat any edible aliens that they capture.
First Appearance: Amazing Mystery Funnies #16 (Dec 1939).

Nelson, Nicki, Capt. - This is a member of Space Patrol. His partner is Kodi.
First Appearance: Amazing Mystery Funnies #16 (Dec 1939)?.

Pan-Asia - This was the asian federation formed under the rule of Manchuria. It was controlled by an emperor and is very hierarchical. It opposed the Western Alliance.

Satan Rex - Years before Einstein presented his General Theory of Relativity, the man who would become Satan Rex had developed the same theory. He was ridiculed by his small-minded colleges and swore to take his revenge on the world. He turned some of his theories into reality, giving him nuclear power and other technology far earlier than the rest of the world. He gathered followers to him (later known as the Sons of the Atom) and built a power base in the City of Mists in Tibet. Years later, he sent the Sons of the Atom to destroy Dr. Jon Linton who was developing technology too similar to his own to allow to live. Linton survived the initial attack and took the fight back to the City of Mists. With the help of a lover of freedom within the city (Dahl Lak) he was able to penetrate the Green Mists protecting the City of Mists and set Satan Rex's plans back considerably.
First Appearance: Amazing Mystery Funnies #16 (V2 #12, Dec. 1939).

Space Patrol - This is the interplanetary police force operating within Earth's zone of control (mostly the Solar System). Much of the Space Patrol is based on one-, two-, and three-man patrols with considerable license to deal with interplanetary criminals.
First Appearance: Amazing Mystery Funnies #16 (Dec 1939)?.

Toyat, Dr. - This was a scientific mystery criminal that the Iron Skull fought in the 1970's. He specialized in creating giant, cannibalistic women.
First Appearance: Amazing-Man Comics #7 (Nov 1939).

Underwood, Tommy "Moose" - This enormous gangster was a member of the Purple Dragon Gang for many years and often served as bodyguard to Al Avison.
First Appearance: Amazing Man Comics #17 (Nov. 1940) - There may well be an earlier appearance.

Vulkite - This is a wyvern-like creature inhabiting Mercury.
First Appearance: Amazing Mystery Funnies #19 (Apr 1940).

Watson, Jacob - This is the scientist who took a nearly dead soldier and inserted into him a robotic skeleton to create the Iron Skull.
First Appearance: Amazing Man Comics #5 (Sep 1939).

Zuraw, Dr. - This was a scientific mystery criminal that the Iron Skull fought in 1970's. He developed a method to temporarily paralyze the minds of radio listeners.
First Appearance: Amazing-Man Comics #14 (Jul 1940).