I got married at EDR on April 27th, 2007, and used an outside photographer who also happened to be a guest at the resort for 3 nights. We didn't have any issues with this process. In fact when the WC asked us if we wanted to use the hotel photographer, we just said "no- we're all set" and that was basically it. She didn't ask us any questions or mention any fees. We never told the WC (or anyone else at the resort) which one of our guests was the photographer, so the resort really didn't know how many nights they stayed. We didn't have any guests on a day-pass, so I can't comment on how that worked.
Good luck working this out!
I'll also add that I loved the EDR! Yeah, the beach is small and not as gorgeous as some other areas in Riviera Maya we saw, but the rest of the resort more than made up for that. I loved that the resort is huge! Lot's of opportunities for us to walk and burn off the high-calorie meals/drinks we were eating. Plus, by staying in castita's we were far enough away from our guests to not see them if we wanted, or we walked 10 minutes down to their area when we wanted to see them.