As far as i know ghost shrimp don't eat algae.. they are scavengers.
There are other types of shrimp which do eat algae, including amano shrimp. They are generally more expensive.
AquaSeaFoam is correct. Ghost shrimp do not eat algae. They're still great tankmates!
I rarely see my amano shrimp in the 55 gallon planted tank. There's one girl holding eggs right now, so I see her nearly daily while she's eating away!
Amano shrimp are great, if you can find them. They eat algae, but like ghost shrimp they're also scavengers. They'll eat anything they can get their little pincers on. So, if you want to get amanos, you might do well to get some cories or something else that can scavenge faster than the amanos do, that way they're kinda "forced" to snack on algae instead of other food droppings.
Mine are almost always swimming around my 20g looking for something. It's hilarious when I drop in a sinking tablet for the cories, and one of the little 1-2" long shrimp comes over and tries to pick up this table that's half as big as he is