A few years ago, I was sitting and chatting with my dh's aunt....she loves WDW and used to go quite often when her kids were younger. They would put their swim stuff in a carryall bag, and get a locker for it at MK. Then, midday, they would take the bags out, and head to the Polynesian, for a nice mid-afternoon swim! I told her that was no longer allowed.....well, she didn't seem to much care. She said they had always done it and were planning on continuing the practice when they went down with the grandkids. She hadn't been in about 15 years at that point. I told her she could very well be asked to leave the pool area, she told me they would take that chance.
They didn't stay on-site, but in a less expensive hotel a few miles away. I never asked her how it worked out....just avoided the subject. I get too annoyed with people that feel it's okay to do this.