I dont think it should be a problem. People who keep ghost shrimp as pets have observed them eating tiny bits of uneaten fish food that sink to the bottom, and they will also eat algae. (maybe algae wafers or some such thing) I dont know how to help you about the smell though . Maybe someone else will come up with that one.
Had that problem myself and I think it was because I put too many in.... Be sure not to leave dead shrimp at the bottom of the tank and I found that doing mini partials on a regular basis helps. Sure others may have some more advice. This is just based on my experience!!!