I don't think they're fap material, really. The outfits and camera angles are certainly sexual, but I think that's to make them feel vulnerable. Like Drebin keeps saying, Snake is "cleansing" them of their surface emotions to reveal the vulnerable inner selves that the shells were made to hide. (Which really doesn't follow--I don't know how you make a crazy person not-crazy, but beating the hell out of them wouldn't be on my list of guesses--but whatever.) When they come out of their suits (which aren't sexualized at all; they even have male voice actors before they come out of their armor) it certainly isn't titillating in that way; even if you do think "wow, she's hot" more importantly you think "wow, she's pathetic".
But I might just be being generous. This is the game where nearly every female character outside the B&B has her shirt unzipped for no reason.
Thanks, SchildConstruct! Hope it's not too much like an actual asylum, though. Once you get past the novelty of being around crazy people, those places are boring.
Edit: Yay, I can post without permission now! But I'm still wearing a creepy anthropomorphized steak.