Yeah I use to keep my copepods in the sump so they could thrive without harm and they would get sucked up into the tank. Worked pretty well.
I got tired of the sump noise a few years ago and plumbed the overflow/return through the walls of my house to an outside shed. It was one of those things that I thought about for years and finally did. So awesome! My tank is almost completely soundless now, and I have tons of room and easy of access that I didn't have before in the sump.