Well Dr. Gero is obviously crazy. He stays in the Labyrinth, where his only patients are Gaudi, who eat sentient species. For some reason he really likes the giant cockroaches. Perhaps one of them saved him from a burining building when he was young and he was raised by them ever since. Doesn't explain where he got the medical training, though.
Of course, if one pill can cure any sickness or injury, being a doctor can't be that hard.
Nurse Hamachi is probably also crazy, judging by her ghost paranoia. Well, maybe I only interpreted it as paranoia. I don't think she ever said "Holy ass fucking titties I am afraid of ghosts" (or something of the like), but it's not like she ever went to get the Cure-All herself. Alright, who knows how she feels about ghosts, but they are a big deal for her. CRAZY!!!