[Koha] Erotic materials (some say pornography)

The obvious solution is of course is to have a completely separate site/database; can multiple Koha sites share the same Patron tables? Can you then filter access per database based on Patron category? The main problem with this approach is that of course it's not a black-and-white judgement call but shades of grey - from "a few soft-core bits" vs "pretty racy stuff" vs "outright pornography". So ideally the whole collection could remain in a single database and just be classified using an appropriate field. Based on such a field, is it possible to toggle visibility in the OPAC based on Patron category (disallowing anonymous visitors of course)?