Nope, the Plutonium Boss is not the Hero's pet frog (Fred), nor is it even a frog... though I think I've only gotten to him once ever, so I could be wrong. It's a long and hard game with no saves and no passwords, thus one really needs to block out an entire day.
Still, there are at least 3 mutant frogs in the game, which surpases CT by maybe two (I'm not sure how to classify the non-Glen frogs in it).