There definitely is a cabana at the outside waterpark area. We haven't been to the Lodge since last August, but at that time, it was available only to the "Family of the Day".
Every room can enter via a ballot obtainable from the front desk, and then you drop it in a big drum by the indoor waterpark early in the morning. They pick one ballot and that room is the "Family of the Day" (as long as someone from that room is actually present at the drawing....you're not there, no prize, and they draw again).
We were super lucky and won on our second night

. Not only did we get the cabana for the day (complete with a tray of snacks and an assortment of drinks), we also got a whole whack of other great prizes like mini golf, refillable cups, a deck of cards from the Trading Post, free Cub Club activities.....some other stuff too, but I can't remember it all without looking it up. It really was an awesome prize to win.
The funny part is.....hardly anyone enters

. The staff there said that they get very little response since the ballots can't be placed in the drum until early morning, and you have to be present to win (many families can't be bothered). On our mid-August visit in 2012, there were only 3 other ballots besides ours in the draw on the day we won.....and the Lodge was at capacity.