Its definately fine if you know it gets migrated. As for against the FAQ, I usually tend to hint at an answer when I comment to why I am closevoting a post. Some questions are actually interesting enough that I post an answer, then ask, and occationally when I really KNOW I oughta comment, but its too long, I post it as a community wiki.
There's no official policy, and I think its a good thing. You're taking a calculated risk - a closed question can potentially mean lost rep should it be deleted. Trying to answer the question might also help get ideas on how to save it. On occation, halfway through the answer, you realise its an unsalvagable mess, but you learn something new.
I guess as with anything, if its an interesting enough bad question, its worth trying to answer, simply for the learning experience. Someone with a pattern of bad questions will get question banned anyway ;p