I think they'll do a pretty good job of it, unfortunately. If you don't have a refugium as a back up 'pod/infauna breeding facility, I'd leave them out of your tank.
I had a six line in a small tank for a while. Even though the fish were well fed, he was constantly on the hunt. The bristleworm and pod population definitely decreased.
I've got 4 SL crabs in my tank. At night the pods are all over the place. My SL crabs stay on the rocks and I've never seen them in the sand. I can't say that they've depleted any infauna in my tank.