Yeah, the guy's DNA has been royally screwed with. Of course, he started it off:
EDIT: I've been posting a lot of full pages. Is that alright? If not, I can go back to posting single panels. I just wanted to post that great fight between Hank and Logan for full effect and illustrate a short history of Hank's changes in this post for those who haven't seen them.
After that, Quasimodo drained his life energy, turning him from grey to blue. His blue form is so iconic, though. Then Carl Maddicks had to experiment on him:
Cool, you're human again! Then, like you said, he had to make a kiss interception from Infectia meant for Bobby, destabilizing before ultimately making him blue and furry again:
But Sage jump-starting his healing factor when he was mortally injured, making him a cat-man was when everything really started. You're right, he does need a clean DNA slate, but I wonder: the serum just draws out what's already there, right? Maybe he was always destined to be blue and furry.