There are a lot of 'specialist' shrimp products out there for the fanatical shrimp breeder, often very expensive and with quite tenous claims as to what advantage they give. They may not all be snake oil, but as long as your substrate isn't leaking large amounts of ammonia or anything I wouldn't worry about getting specific 'shrimp substrates'. Unless you've got some ridiculously expensive breed of shrimp, in which case by all means carry on