Here's the thing about us guys: we can't pee with a hard-on. If "Angel Lust" is real, and a man does get hard while hanging, it would probably prevent urine from flowing, at least for a while.

Another thing is about how an erection works. Blood flows to the penis all the time. The difference is that some valves close, preventing the blood from flowing back out as efficiently. That's why cock rings work (though I've never been interested in choking my chicken so literally). If hanging triggers the erection, but death prevents the valves from re-opening, your penis would remain hard even as the rest of you goes limp.

Whether any of this results in pleasure is debatable. But then, autoerotic asphyxia is a thing, so there ya go.