It's been done. I've seen a solid kayaker roll my stiletto on the skykomish at the big eddy takeout. took him 2 tries and he could barely do it.
The aire force is rollable, if you search boatertalk, or read the old posts in the rafters forum, there have been several threads about it.
But practically, it ain't all that useful. We were talking the other day about how different swimming is in the ducky. once we're out of the boat, yeah we're swimming, but we've got 700lbs of flotation, we've got a huge soft fender to ward off rocks, we've always got air to breathe, and we can self-rescue.
A hardsheller, though, once swimming is in a lot worse situation. When we separated from the boat, only then are we really in the shit. I may swim a lot, but I also almost always keep my boat, so it doesn't usually end being as long or as dangerous a swim as swimming out of a hardshell.