My main concern would be that the windsurfers will not know the rules...
Given that the Windsurfing Competition Rules are somewhat different than those for sailboats (see RRS Appendix B), before I asked if they knew the rules -- I would ask if we do.
But I don't believe rules aren't the issue here so much as sharing the water. I race in a club where some sailors think that other boats shouldn't be on the same course as their fleet. That kind of exclusionary thinking is very damaging to our sport. Most clubs I see are getting fewer and fewer boats racing. The last thing we need is to drive people away.
If sailboarders want to join you, be open; be friendly; be welcoming, and invite them along. Give it a try. Understand that the water belongs to them just as much as to you. I bet it will expand your horizons as well as theirs.
Regards,
Eric