I hate to be a stickler here, but well I guess I am.
First off it's CO that is the dangerous gas and for the most part really isn't a significant risk while wakesurfing. Certainly there are risks associated with CO poisioning and boating, but not anymore significantly for wakesurfing. In many studies, due to the stationwagon effect, the rear seats of the boat have higher concentrations of CO than where the wakesurfer typically rides.
Notwithstanding, IMO for all watersports behind a boat a PFD is a wise choice.
In respect to FL law in particular, they do follow most of the NASBLA recommendations and my understanding is the specific language is:
"No one may water ski or use another aquaplaning device unless they are wearing a U.S.C.G. approved non-inflatable Type I, II, III, or V personal flotation device (PFD). Inflatable personal flotation devices are prohibited. "