I'm not a sat diver but I know a few. ;-)
My 2p is I think the HEV on a dive watch is rather unlikely to be activated during a commercial divers work nowadays as their environment is very closely monitored throughout decompression, so any He inside the watch will have time to expel naturally.
Given that the vast majority of HEV-equipped watches will never see the inside of a compression chamber then you might wonder why so many of them are thus equipped...
R