For that matter, my swim team used to do swims at 5 AM in an unheated pool at the SC high school, every day of the school week. That said, you tended to warm up FAST because you were swimming, but I can testify that that water was C-O-L-D. And I never got used to it.
I dunno. I just think it's unnecessary. When the water's warm enough, there shouldn't be a need for a wetsuit.