While I can definitely see how this could be considered rape, I never thought of it as such. Angel seems to be appreciative of every visit, if only because she is bored or lonely otherwise. Sure, she might not necessarily be able to vocalize her consent, but I'd think that reciprocating their actions should speak that for her. She's not happy, obviously. I think that has less to do with the mandatory sex and more to do with how Medic treats her, and how she is trapped in that dark place, and how she can't remember who she is. I think also that she cares for the men, and is affected by their stress and guilt. It must be hard. I hope she gets a happy ending.