It's not usual. WRSC beachcats race with the 5o5s all the time, including bigger events. Very good racers and fast. Same course, they start afterwards. We had teams go to the 5o5 mid-Winters at Ft DeSoto State Park last February. I believe they invited A-Cats to join them. As you can expect, there are club members that "swing" both ways including F16 teams.
We also "club" race with Chesapeake 20s same course and Albacores & Flying Scotts with a shorter "A" mark on the same course.
The distance race weekend before next year's nationals gain a lot of attention for the beach cats. Nothing like starting last in a fleet of 150+ monohulls and big multihulls only to be contending for line honors after 33 miles. Some monos get nearly an hour and half head start with 5 min rolling starts for the rest of the fleets. Beach cats park on the beach right in front of the party tent. It's all fun.
We just missed a nice event up in Long Island Sound, American Yacht Club Heineken High Performance Dinghy Open, that featured Fireballs, Viper 640s, 5o5s, RS K6, 49ers, Flying Dutchman, and Moths. Ohhh, there were F-18s also.
It's not as big a shift in policy as you may think.