We've only gone down in the fall, but are going this summer - I can only imagine how hot it'll be! but many of the venues have huge ceiling fans to try to keep it cooler, plus there's usually a good breeze coming off the beach.
I'd incorporate fans into your wedding planning. whether it's folded paper fans, or a program fan for the ceremony, those will be good for your guests. and a shaded ceremony location for your guests if your ceremony is outdoors would be best too. that sun can be intense! plus cold bottles of water and such.
I'll pop back over here after our trip in June and share my thoughts if noone else comments on a summer wedding.