I've heard the turtle legend, but that's the only time I've heard about someone getting out. I've seen enough bad swimmer recircs (out of boat) that if I end up in there again, I'm holding my breath and pulling immediately. It terminates in a pool after all (just watch out for the sieve below it).
I believe Rolf paddled back in there intentionally once and he ended up pulling. Legend has it that he has a 4 minute breath hold, so if he can't get out, not sure who can.
The craziest thing I ever saw there was one of those riverboarders,aka dick-draggers. He went right for the meat line, just plugged in with little speed and I thought, "Oh no, he's going to... swim?" The guy was right there in the gut of the hole. He reached downstream with his board, and just kept kicking with his fins and he just slowly worked his way out to the boil line and out of the hole.
It made me wonder if there was a way I could somehow fit my feet into the boat with fins on.