No native fish are algae eaters, so for natives you would be looking at snails or limpets.
I have some shrimp with my Borneo suckers. They eat basicaly the same stuff as the shrimp (diatoms and fish food) but can suck onto the glass where your shrimps might not be able to get to. Won't have much, if any impact on green algae though.
Your other option in an unheated tank could be a Chinese Algae Eater. I havent kept them, but from what I have heard, I would be worried about them harassing the shrimp, and they eat less algae once they get a bit bigger