the purpose of the crossover rule is to protect someone who signed up for one fandom from being thrown a story which deals with characters and situations with which they are totally unfamiliar.

I think it's relatively safe to assume that anyone who signed up to write a TNG story would have some familiarity with Spock Prime. But, if you felt too much like you were playing a trick on someone by nominating that story, you can always nominate another story for remix.