Hey Agordon, A lot of good questions that I'm curious to hear the answers to! One thing I think I can offer...the doctoral candidate was male. The shrink was female, but every time Gideon refers to the doctoral student he says 'he.' Plus, Gideon admitted to having an affair with Anne on their trip to NC to get back at Lucas.
I think you could be on to something though. I was wondering if it was Dr. Lucas himself that had abused Gideon. Lucas is a pediatrician, so it's not too far of a stretch to assume he was doing some type of clinical rounds in child psych as part of his training. Or, he could have been the one that examined Gideon and covered it up, too. It's not really clear yet what Dr. Lucas did, but it did cross my mind that he might be the perpetrator. He's the right age.