Umm, fairly certain that Ghost Shrimp don't eat fish waste, unless what you meant was as in leftover food. Ghost Shrimp never bred in my tanks so it's probably not likely they will breed in yours but this is just my experience. They are scavengers so they eat leftover food.
Also you may want to have small hiding spaces for them, Betta's tend to find shrimp as tasty snacks. These guys also have claws unlike most shrimp like Cherry and Amano which are more often marketed as the algae eating shrimp, which is what they do. So it's best to not house these two kinds of shrimp together since the Ghost shrimp is a little more territorial and will fight the defenseless cherries, however some have had success with this.