I just visited the Yankee Airboat site,
http://www.yankeeairboats.com/ according to the article the boat was 15' 6" long. They list a Yankee 16 boat, which has a capacity of 2000 lbs. I would think 4 rescuers plus a patient would be within this capacity. ( 5 X 200 lbs( avg estimate, probably less then that) equals 1000 lbs). The website is short on details though and 2000 lbs in sand bags loaded on the deck of the boat is much different from 2000 lbs in people and equipment which would have a much higher center of gravity. This looks like a small company making what amounts to a not so small product. A little more detail in their written specifications and probably some more testing will go a long way to avoiding this type of accident in the future.
I hope the rescuers are sheilded from liability personally (Skip ??) in this case, these people did not get up in the morning and say I'm going to kill someone today, they're victims here also, at worse they were victims of faulty or no training.
Hopefully some good will come out of all this. Some rules among rescuers that if you place a patient on a boat that some type of floatation device should be used that will protect the patient. If the patient must be secured to a boat that someone is assigned to be with the patient at all times and in the event of a capsize that the patient is automatically released or at least a quick release device is used. These boats should be put thru their paces before being used (or bought for that matter). I would think tests for these types of situations would be pretty easy to develop and perform. Especially being loaded in real life situation and hitting a 12 to 18 inch wake at an odd angle.