I remember Wishy brought Mickeysgirlz and her two DDs into Kidani Village’s pool as guests, so I woudl think that the policy would be the same at BLT. I hear BCV’s pool is heavily-guarded, though, as it is a mini-waterpark, so you might have a little more difficulty getting them in there. Yet if you are with them upon entry, they typically only ask to see one card.
I stayed at BLT back in September, and I was never carded to get into the pool at BLT or the Contemporary. However, I did only go swimming at night when there were no lifeguards. The important thing is that you have to have your room key to get back inside from the pool, as well as the beach. Though the cards didn’t always work… we witnessed some boys with a key not able to get back inside (we were kind and helped them out), and my sister and I got stuck on the beach late at night and had to call a CM that was cleaning up around the pool area to come over and let us back in.