Yes Go Pros are everywhere particularly in the skydive world. On any given load I fly there could be seven separate HD cameras on board the skydive plane I fly. I've often thought that if there's ever an in flight emergency then I'd better do my best Chuck Yeager impression and stay frosty because it's all going to be on Youtube the following day. It would also make the accident investigation easy!
The Instructor did a good job in recognising there was a problem and opened the guys chute for him but to be fair AADs are pretty standard these days and it would have fired and opened his reserve for him long before he hit the ground. Not that you want to wait that long.
I've seen a couple of AADs fired. One was a girl on a first jump. She made a shocking exit and her main got tangled and she started spiralling. She ignored all calls to pull the reserve. I was on the ground watching and she got very low to the point that I knew she was dead and was starting to look away. But the AAD fired and she lived. The crazy thing was that she didn't seem to realise how close it was. She came in all smiles! Those of us in the know were shaking!
