Certainly, if it's nothing more than fellatio at gunpoint, your hypothetical prostitute has not been raped, IMHO.
_____________
Let me say it out loud. Oh my God.
I have, until this comment, given you the benefit of the doubt as a well-meaning but sadly mistaken person on this topic. After the comment above, I cannot give you that benefit of the doubt (and I know that means absolute jack to you). You have gone from having a misguided notion about rape to what, I have no words for.
I thought at first you were arguing from a religious stance, and just confusing hating the sin and putting it on the sinner, but that is clearly not the case. There is no religious person on this planet who would suggest that a prostitute forced to fellate another at gunpoint has not been raped.
In my apparently twisted way of thinking, that doesn't rise to the level of "rape." Rape isn't a $10 crime. Others apparently disagree. Go ahead and call me what you want but, that's how I see it.