We have integrated with the monohull fleets fairly well, but my advice would be having at the very least, a different A mark. A different course would be preferable, and certainly never race DPN/PRHF conversion. If you are easing your club into cats, do it slowly, they are just plain different from us in logic and philosophy.
Another thought is to have an "Adopt a monhull skipper day" and let them race with you. Swap boats occasionally in your local races. Crew for them. Have them crew for you. All these thngs will keep the cats in a good light with the monohullers, and unfortunately with all the beaches going private, we need them. But conversley, they need the numbers, and that would be us.