You should keep all predators out of your sump. Unless you set up an area where they can't get to. They call it a refugium because it is is supposed to be a safe place a refuge from predation. So things can breed in piece.
I add Macro algae like Caulerpa and chato, Mangroves, I do a Cryptic Zone with less light and live rock. So I cultivate things like Sponges to filter my water. In the past I have added in a small section like mushroom right below the output into the sump. As food drops in it is eater by them. They also like to use disolved organics in the water so the help to clean your water. Xenia also work well. Both can be removed regular as a means of nutrent export.