PS, thanks for the kind words. I'm not necessarily that much more experienced that you are--this is my first slave, and I've only been actively playing this way for about 18 months. So don't be too impressed with me.
Your points about the way rape victims may avoid acknowledging what happened are good ones, but my slave doesn't seem to be in denial about being raped. He's mostly struggled with trying to stay in control. He told me that for 14 years, he never let anyone get close, and never told anyone what happened. Within two days of giving up control to me, he had begun talking to me about being raped, and now he's told his father, his brother, and a friend. So for him, admitting that he's not in control with me seems to have made it possible for him to admit that he wasn't in control of what happened back then.
He's got some complex issues with anal sex as a result. The two times we tried to have anal sex doggie style (which is my preferred position), he's gotten extremely scared, and the second time started screaming in pain despite my going slow, loosening him up with toys, using tons of lube, and not actually getting into him. He was held face down during the rape, so face down sex makes him clench up so much that he feels pain even though objectively he shouldn't. The next time we try it we're gonna try it face up, which he says feels safer to him.
I decided to go a lot slower with anal sex, so I've been having him wear a butt plug, which he likes. Last night I tied him face down and did a little pain play on his ass, mixed with lots of caressing, tickling, and other sensation play. At first he was really scared. Then he asked me to move the pillows (turns out the rapist pressed his face into the pillows), and as soon as I did that, he relaxed a lot and just let me work on him, which he found very arousing. I would have liked to go further, but I don't want to press him too hard; I figure small steps to desensitize him are more likely to have lasting results.