From what I was told by someone who does it regularly it is a lot less dangerous than it looks and not really more dangerous than many other lifts or ice skating in general. It's down to the physics and if they are rotating fast enough to get lift off then the girls head won't hit the ice unless the guy lets go and even then a lot of the force would be disappated in sliding along the ice.
It's not 'safe' exactly but then nothing is.
The worst part is the start and stop - although less so if they start and finish on the ice. Didn't Bonnie bash her head trying to do a standing start which is more difficult.
The helmet is probably as much to do with instilling confidence in the girl to try it.
I agree it doesn't really have a place on this show though or at least I wish it didnt'.
It's a lot easier for a girl to pull off a flashy looking headbanger lift than to do an impressive toe-loop.

I suspect that's why we get them and the other flashy lifts