They're pretty strict about not being around GF too much if there's another wedding taking place (don't want to get in the other bride's way and visa versa). However, Randy's pretty aware of this and from what I've heard, does a great job of getting shots regardless, without intruding on anyone else.
Randy will take pics anywhere, from what I understand. We wanted to do pics by the GF too, but we had lunch reservations we had to get to and it was just too hard for us to get from Yacht Club to GF and back to Downtown Disney without the rest of the wedding guests waiting around for us for another hour. I think really the locations are only restricted by how long of a package you have with Randy.