the moss is a spawning ground for them. It will attract them. You don't need the strawberry box per-se, but it does keep things nice and tidy. I got the idea from a salt water set up where they do the same thing. It is called a "pod box" where they stuff the strawberry container with cheto so that the pods can breed with minimal disturbance from the fish.
I haven't tried in with a DP but the theory is the same.
I have done the java moss and shrimp in a DP tank with much success and others have also. Just minus the strawberry container