It seems Steve and I are in the same category. I'm a trained lifeguard (for over 20 years), I train lifeguards, and I'm Rescue Diver certified.
Of course, much of the emergency procedures are similar and only vary in the type of equipment that is used and available, and the first aid practices (CPR, etc...) are virtually identical except in a few scenario specific details.
Perhaps the strongest similarity is totally mental, or perhaps more succinctly, psychological. In both endeavors, one must be mentally prepared for the situation. This involves rehearsing a situation and its variations multiple times in one's mind and in practice until it becomes second nature to respond properly. This "mental toughness" is by far the most important aspect of reacting correctly in an emergency situation, and if the training is thorough and competent it prepares the responder well. This is true in both lifeguarding and (rescue) scuba training.