Went to the 7/18 party. At least at our party the CM's were pretty strict on checking the wristbands. The wristbands were bright green and opaque so it would be hard to fake. They were checking for wristbands at food carts, lines, and even people walking around.
They have CM's stationed at certain points throughout the park and were ushering people without bands out of the park. I would say by about 11 it was pretty dead. We waited ten minutes for mine train, everything else was walk ons.
Loved this more than the halloween party. Similar atmosphere, but free snacks instead of the candy trails.