Swim vests, noodles, and "Swimmies" are allowed. Floats and such are not. Tubes are allowed in SAB ONLY in the lazy river area, although if it gets too crowded, the lifeguards will not allow people who brought their own as opposed to renting WDW's to use them.
It's a safety issue. The lifeguards can not see the water under most floats and rafts. That's why noodles are allowed-they are slender enough to not obstruct anything. That's also why they have switched to clear tubes at SAB.
Some of the WDW pools get much too crowded to use anything larger than a noddle or waterwings in.
Anne