We were at both parks last year, first week in September. My mom had also read we needed them as people claimed to be burning their feet..
Well, I felt they were not needed as "water" shoes. Flipflops to wear in the park, to slip on when getting foods, bathroom etc.. I find necessary.
But in the active part, swimming, going from slide to pool, to slide etc.. no.... yes the ground was hot, but in most places where there is water nearby, the concrete is wet, and you wont burn.. I did see some open areas and they had like little sprinkler things going off to cool the concrete down.. Also if you are barefoot and need to walk from A to B and B is waaay off, then we would just hop in the lazy river and "ride" over to the other side. Both parks have the rivers going around the park. Lines for water slides are also issue, like I said ground is wet.
My only advice about shoes is DO NOT just dump your bags and toss your shoes about.... They will be "gone". I was with the kids for a short visit and we dumped our towels on the rock wall near the wave pool and kicked our shoes off. There was a large family.. ( they seemed local to me) and I think it did not appeal to them that we put our stuff near them.. Well when we got back all 3 pairs were tossed about... my son's we found in two spots about 15 feet away.. my daughter's also some where nearby tossed about.. Me as only adult and driver only found one shoe.. Great spent 50 on a pair of disney cros flip flops at the shop ( BTW blessing in disquise as they are now my fav and most comfortable shoes!).
Anyways loong story short... hide your shoes and only bring cheap flip flops in.....
either we pissed the family off ( by gut feeling by their dirty looks and "we dont give a darn and didnt see what happeded to your shoes" response) or kids like to mess with people's shoes. It was not the wave pool tide.... By customer relations some other guy had the same problem.