Right. They are going to let you in for sure with a reservation. They can turn you away for other reasons.
As most have stated, if it's not super busy, they'll probably let you in. I've faced more scrutiny lately, especially when attempting to go to the Contemporary. Not much I care for as far as lunch goes there. But I do buy some of the exclusive records to resell in my record store, and with my AP discount, they're a good deal. There's a store at the Contemporary that is well stocked.
Once, we were turned away. We told the guard we were just going shopping, knew what we wanted, and would be spending at least $300. No dice. So we made a quickie ADR at the poly for lunch, parked there no problem, took the mono to the Contemp, made our purchase (slightly miffed.)
Another time, same explanation, they let us in. But there and the Boardwalk (General Store works for me as well) they've been asking more questions and giving "looks" lol.