I suppose I should pay attention to this thread on a more regular basis, eh? >_>
@Ruk: If your costume has a good deal of spikey and/or dangerous protrusions you'll definately want to have it checked out at the convention. If it does have the potential to harm someone I would recommend covering the points, even if you think it's unlikely, and just taking off the coverings for photos. I know it's easy to accidentally hit people with props/costumes in such crowded situations (try a Cross Punisher!), so it never hurts to be safe!
@Aurora: Judging from the ruling as worded that may be a subject for debate if it's just a mouth-covering style mask, but probably not a big issue. It seems the main problem the hotel has with it is the liability of vision reduction while moving and complete obscuration of the face. If it's a problem I'm sure a yojimbo will (kindly) ask you to reveal your ninja selves, but feel free to don the mask during a photo op! (Just don't move, heh)
(Note: I am not an official source, just a yojimbo offering my thoughts on the rules. If anyone who knows better knows I am wrong PLEASE correct me!)