I am not aware of a "beach cabana" on WDW property. There are some on Castaway Cay, Disney's private island through the cruise line.
The deal is that you are not permitted to play or swim in any of the lakes, around the beaches that they have anyway. Unfortunately there are critters in the lake - and the lakes were closed years ago. I remember when we used to swim in there all the time - but the last time I swam in the lake in the early 90's, I was bit by something - didn't break the skin, but I felt it and it scratched my skin. Later that night, I saw employees working to catch a baby gator around the dock. Yikes
So... a beach cabana may not make that much sense. The only DVC place I have seen cabanas has been Grand Floridian (but tbh, I haven't really looked at other places to see if they exist. Not sure about beach club???)