It's not real common, but you see it done occasionally. I had a section in my sump for plants at one time, but didn't do much for nitrate control. I've read that the best way to use plants for this purpose would be to use common, fast growing house plants and just put the roots into the sump.Is this a common thing in freshwater sumps as well?
Regarding shrimp for food, I figured by the time the pump took them in and spit them out in the tank, it wouldn't be live anymore.
There might be some benefits, I just don't know of anyone who's kept it going long enough to prove it out.