I don't know how a drysuite would act in 30+ degrees but a wetsuite at around 20 degrees gets quite hot in quite a short time. Are you sure that a drysuite wouldn't get even hotter?
Dry suits get as hot or hotter than a wet suit, but once you are in the water, even warm water it's fairly comfortable. I considered using mine to take shots of birds but quite frankly I don't want to even think of what trying to clean off that muck would be like. The dry suit actually costs more than my camera. I really need to find less expensive hobbies.