Robert--
I agree with you. I think he should choose a kayak just like anyone else does. Whatever kayak he chooses will need to be outfitted to give him a tight fit that he can still escape from. I'm not sure that footpegs will be an issue. He does have the advantage, as a diver, of being comfortable in the water. I seem to remember groups that specialized in helping disabled people kayak, maybe around the Boston area. I'd bet that he is not the first person to confront these issues.

Mike