Good on you! You seem to be defying the eel's digestive system haha..
I don't have any evidence to back up whether cooked or raw is better for fish, but I reckon just keep it natural. In the wild, the fish is never gonna get a cooked meal ever, so it's probably not designed for that kind of food. If you compare a cooked prawn and a raw prawn, the cooked is much tougher than the raw, which tends to be mushier, so Henward might have a point there about their digestion. Besides, raw prawns aren't expensive, so why risk a fish over a few bucks?
Just my 2c..