Most of the time if the fish comes from an invert only system it shouldn't bring a parasite into your aquarium. The problem is that many LFS
's run a central system so water passes from tank to tank. Parasites like ich can encrust on the carapace of shrimp and other inverts and then infect fish tank mates. I have never qt'd any of my inverts and never noticed a parasite problem after adding them.
That said I would make sure there aren't any noticeable parasite problems on the fish elsewhere in the system. If the fish look ok and the shrimp seem healthy I think you would be alright.