Though this is only a resort guest perk, Disney does not do a very good job in checking. Just last trip the couple next to us a H&V commented that they were surprised that MGM was openned so early and I asked them if they were staying on property and they said no.
I recently stopped going to EE because the crowds are so bad during this perk now. We used it in May most of the time, then tried it in July and only did it twice (MK and AK) and decided it was way too crazy. We were never asked to produce our room key. We then gave AK a shot again during our September trip and my adult daughter didn't have her room key with her, but didn't matter, because no one ever asked. (Of course, we made a big mistake trying to do EE at AK in september--what was I thinking). So as we prepare to leave next week, you won't find me at ANY EE during this 10 day trip.