I just got back from a trip to the Outer Banks. I had my 18" wheel QTII Laredo on the sand a few times with no issue. I went on all of the little back roads, and some that weren't even roads all without airing down the tires at all, I left them at 40psi. I heard the traction control a few times but it just went everywhere without caring.
I did hit a puddle that was a little deeper than expected though. It started out fine but kinda dropped off into a 2.5 ft. swimming pool of water. I was going about 15-20mph and water was over the window and roof. It was pretty cool, the wipers did a good job of getting the sand off so I could see again.
And no hydrolock, even with a constant flow of water over the hood and grill for 2-3 seconds, the filter wasn't even wet. There was a lot of sand and debris in the airbox but it did take it like a champ.
I really doubt you will have any issues with the 20" rims in the sand. Especially if you air them down a little.