As I'm planning a tank like this, I've also looked into the question. it hasn't really been resolved, but you can imagine the fry are going to be much easier to eat than the adult shrimp. The summary I gained from reading was that you should establish your shrimp colony first. That way, the shrimp colony has the numbers to sustain any predation by the fish. They won't eat all the shrimp and the shrimp will be confident in numbers. I suspect if you just added a few shrimp to a minnow tank you'd never see the shrimp again. By giving the shrimp a head start you should be able to achieve a balance in your tank.