When I lifeguarded at Blizzard Beach for a few weeks during my college program back in 2002 (note the date, so things could of changed) the rule of tumb is that if it can be attaced to the child it (with a zipper, snaps, clips, sewing in, etc) was ok. But if the child could just slip right in and out (ie water rings) then they could not.
Note: Arm floaties/water wings are ok also even though they slip on and off.