They eat dragonfly larvae, mosquito larvae, and tadpoles, so I don't see why they couldn't catch and eat feeder shrimp. I imagine the difficulty would be in keeping feeder shrimp alive in the sort of mess a duck tends to make when it doesn't have a large pond.
EDT: that's assuming you're leaving them in there as a breeding population. If you're just occasionally buying shrimp for treats and they're not expected to survive, who cares if the water's too dirty?
I dont plan on breeding them I was just considering buying some once in a while as treats for them if they could eat them i know they can eat feeder fish which i plan on getting them some of those soon for them right now there absolute favorite treat is peas they go crazy for them as soon as they see me walk out back with the bag of peas they all start going crazy and race to there pool lol Im also planning on throwing some crickets in there cage when I go buy some today for our bearded dragon