I think there are good reasons to publish the JCR types. Maybe the best reason is to expose modeshape-level plugins (e.g. technical metadata sequencers) in a sane way, without needing  fcrepo-specific knowledge.
 At the very least, I don't think the nt:* types are harmful, and if we wanted, we could hide them behind our own vocabulary (although I suspect it'd look suspiciously similar to theirs..).