Interesting question--one for which I tried Googling. The answer seems to be no, but the water from the store may have ich in it, so purchasing ghost shrimp seems to be an exercise in caution as well.
The fish have all been ich free since last Friday, but the shrimp are looking decidedly spotty- probably because we inspect them so much... like if you watch anything too closely it starts looking weird?
I just don't want to sound an "all-clear" if I need to keep the salt and temps at theraputic levels a bit longer.
I would keep the heat up and salt levels the same for at least 10 days after the last symptom on the fish. This provides enough time for any lingering parasites to be clear of the fish and their spore stage. Anything less and you risk reinfection, IMB.
Ghost shrimp can't contract ich--no place for the parasite to enter their system.
I never thought of this, but the shell of a shrimp would make as good a substrate to encyst upon as a piece of gravel or whatever. It would be mere chance, though, and not likely.