I think that depends on the resort and the general crowd levels at Disney. Last year we were there the week immediately after Labor Day, reportedly one of the slowest weeks at Disney all year. We stayed at the Coronado Springs Resort and never saw many people at the pool... even during the hottest part of the day. We also spent some time with friends at the Wilderness Lodge pool. Slightly more people but still a lot of room to enjoy yourself in or around the pool... no trouble getting lounge chairs or finding space for a family or group.
I would expect that during July or early August, which can reportedly get very busy at Disney in general, there would be more people at the pools looking for a break from the heat. Of course, I have not been during those times so someone else would have to weigh in.