For the submissive it could be arranged, if she were to know the one arranging it was going to be present.

From my POV as a potential Victimizer, if the victim's partner were to contact me, and arrange the situation. I would take any information about the victim that I could gather. To ensure safety, would insist that the person arranging it were to be present, with or without the knowledge of the victim. Thus achieving the element of unknown as the 'Rapist'. I would also need some sort of verifiable poof that the 'victim' had consented to the overall situation. Video being the most reliable form I can think of.

ID