Ghost shrimp are difficult to breed. From what I understand, the ghosties you buy in the store are all wild caught, not raised. I have had bunches that were egg carriers but never any successful hatches. From what I've learned they need exact temperature, moon phases and salinity changes (a.k.a. "Nature") to help the process. I also think they need saltier water to hatch, or maybe my adults eat the babies so fast they never get to mature in my tank (I do have a lot of them).
Ghosties will have no problem with mystery snails and will even ride their shells and keep 'em clean.