I can now post a educated reply to my own question. A Hustler 950 WILL swim with 22x11-8 GBC Gators!
Finally--I have some forward motion and some left/right control. Seems to swim pretty good actually.
Now to get it watertight. Crossed my buddy's small pond and took on a couple gallons of water. Nothing the bilge pump can't handle, but bearings, and flange seals are next on the list.
I'm a happy camper though. At least I can now cross the crick confidently, and have the tires to pull me out the other side.
I do notice the 6-ply tires ride worse than my 2-ply tires. That's to be expected, and I'm running about 2 1/2 lbs. Gonna try 1 lb and see how that does next trip.
Also can't turn around in my yard anymore as these tires pull up chunks. And it Does turn a little harder, especially at slow speeds.