We had friends with us and used the pool. They asked our guest for his hotel ID. When he said he was with us all we had to do was show our ID once and they were permitted.
When we were there in Sept 02 it closed at 10pm. I think some pools allow swimming after hours but no lifeguard. At Stormalong Bay it totally closes down, no one permitted to swim. When you get there you'll know why. But you can use the quiet pools and our room was right beside one so we lucked up.