As Mark said, the OFFICIAL NAHCA recommended policy(subject to change at any time) is only one start for ALL non-Hobies at Hobie Fleet or Hobie Points regattas if the sponsoring Hobie Fleet wants to.
NAHCA does not allow any non-Hobies to participate in any way at events which NAHCA is involved such as NA's, National's, or Mid-Winters.
Most Hobie Fleets welcome any and all boats.
Here in Hobie Division 9, almost all of our regattas are open. (some people don't like keeping times)

There is a big difference in getting a "start" and getting scored as a Class.
We usually start several Hobie Classes together, but score them separately.
If four or more A Class showed up at a regatta, they deserve to be SCORED as a Class.
If they bothered to actually preregister in time, they deserve trophies.(that goes for any Class)