I think this paragraph will preclude surfers from having to wear a PFD:
Based upon the information available, the USCG determined when beyond the narrow limits of swimming, surfing or bathing area, the device known as a "paddleboard" is a vessel under 46 U.S.C.&2101, and therefore subject to applicable regulations administered by the US Coast Guard and its Office of Auxiliary and Boating Safety, unless specifically exempted.
I can only assume that this will apply to SUP surfing as well, as by their own admission a "paddleboard" doesn't become a vessel until it leaves a swimming, surfing or bathing area. I guess this will make the rule only apply to people that are way offshore.
Seeing as there is no rule in Australia that requires Windsurfers or Kitesurfers to wear PFD's I can't see that this will ever be an issue here, actually after a very quick google, it seems PWC operators in QLD are not even required to wear a PFD (
http://www.msq.qld.gov.au/resources/file/ebc1130cce3ad8f/Pdf_rec_safety_equipment.pdf). So I really can't see anyone forcing a SUP rider to wear a PFD.
But when all said and done, do what feels safe to you. Not much point in worrying about what are rules or not when you are 5k off shore with no way to get home.