I remember reading once, back in the days of oWoD, that a vampire that Capri Sun'd a changeling would have a trip worthy of any 60s LSDathon. That really tickled me, so I generally carry that concept over into other games that don't have a clear answer to what happens when vampires (or other phages) feed on nonhumans. So maybe the RCI gets all hot and bothered after feeding on a lust whamp, or roid ragey after feeding on a wrath one.
As for what happens to the whamp, I'd defer to canon. If they're human enough for Black Court turning, which Blood Rites seem to indicate, then I'd say they're probably human enough for RCI. However, I generally dislike mashing together monster types, so I'd probably have the player choose whether to become an RCI or have a SHOCKING IMMUNITY! (gasp) to the RCI infection. Which could be fodder for quite the interesting story in and of itself, assuming the Red Court is still around to be deeply concerned about this strange immunity...