If the broodstock tank is just going to include things like a pot/tile, rocks, sand, or something simple then it may not be the best idea. It will decrease bio-load in the main reef tank which will add bio-load to the spawning setup which may discourage them to spawn. If you want to do something simple with just a pot/tile and the pair of clowns then no sumps in needed. If you want a tank just for the clowns with a pot/tile, sand, rock, and an anemone then the bioload will still be small, so if you wanted a sump get the tank its own sump or don't get a sump at all. Basically, don't share the sumps.
