I don't have an answer for your question specifically, but we went to the MK early twice on our last trip. Once for an ADR and once for the Keys to the Kingdom tour. They have an entrance open on the far left of the gates and they never asked us for our name or to prove we had an ADR or tour.I feel like anybody could have walked in.
As a PP said, there's nothing to really do other than take pictures, but it is really nice and relaxing to be there when it is relative empty.