Well, I see Dr. Silverback as a cross between the Beast (scientist trapped in strong bestial body but retains intelligence) and a heroic version of Gorilla Grodd (or maybe Solovar). Also, his origin is highly similar to a JLA Elseworlds story which reimagined the Justice Leaguers as half-animal hybrids created by Dr. Moreau. There has also been Angel and the Ape and SAS's Deadeye Chimp.
Some of the others are fairly iconic... Scarlet Shield is a bit like Captain America and Mr X is close to Crimson Avenger or the golden age Sandman. But many of the characters are not very iconic, and many don't even wear costumes! Most of the PSI characters, Kodiak, Kevin Poe, Freakshow, etc. Perhaps it is more realistic that they don't have costumes, secret IDs, etc, but that detracts from the comic book feel of the setting, IMO.
You know, I think Millenium City feels much closer to an Aberrant setting book than it does for a 4-color comic setting. Lots of characters that are not in costumes and don't do the traditional hero/ villain thing, but instead are scientists, run schools, work for the police/ FBI, are common thieves, mercs, and killers, etc. Just a very different feel from the 4-color silver age type of setting.