Hi Hats are tough. I used to collect them when I lived in FL. We stopped because out of every 10 or so we caught usually only one would live.
Keep in mind that these fish were hand collected by me, given the best care and food I could give them, and so it would be difficult to have a much better scenario for getting them to live long term than this. I (and a few other very experienced aquarists) were unable to do so.
In retrospect, I believe them to be very finicky eaters that are supremely susceptible to pacific diseases and parasites. The only way I would try them again is if I had a very large all Caribbean tank. (which could be cool - queen angeles and queen triggers, box puffers, anglerfish, blue carribean tangs, assorted carib wrasses, high hats, snappers) It could be neat.