Lynne, I can only tell you what would make sense to me, but a drifting dive boat can maneuver right up next to a victim, like in a man overboard situation. Same if the boat has a chase boat, like a liveaboard might. Then thermal protection for a deckhand might not play into the situation, because we're in Row, not go.
Lynne, I wanted to come back and expound on this some more. I notice that there are a very few skippers out there who will jump up and say that they are merely a water taxi, that they have no duty of care to the diver once they are off the boat. No doubt, there are some who feel this way, but the vast majority of the folks who proclaim loudly "we are just transport" are the divemasters on the boat, and we've already established that their opinions don't mean much.
I can tell you from experience that the worst feeling in the world is to be standing on the deck of your boat and know someone needs help and there is nothing you can do for them. There may be a few reasons there is nothing you can do, including the deckhand is already out on a rescue, the outboard won't start, or you have divers in the water and can't move the big boat.
Our most recent fatality (which was a number of years ago) I had a deceased rebreather diver, his instructor, and the instructors instructor candidate. The student was dead, the instructor trainer was bent, and the instructor candidate was unknown condition. Mel was out in the chase boat with them, but couldn't recover the body, and I had divers in deco under the boat. Nothing to do but pace.
The most dangerous for a diver is transitioning into and out of the water, that is, at the surface. You're wearing a ton of gear, you're as graceful as a manatee, and when something goes wrong, you are loath to ditch a couple of thousand dollars worth of gear, so it holds you down, maybe head under the water, maybe with no air.
An unprepared deckhand or captain can do nothing but watch helplessly while the diver sorts himself out, or his buddy does so, or he drowns. In this case, it appears that he drowned. The Coast Guard takes a relatively dim view of watching someone drown.