They count- but not as much as regular fish is my understanding.
My reading indicates they leave less waste, however they do take up space- which is also important. Depending on the tank- territory can be a valuable commodity.
I have not heard of any rules of how to count them towards your 1 inch per gallon rule, but if you stick to that and then just throw in a couple of shrimp i would think you would be allright as long as you kept a closer eye on water quality and maybe upped water changes a bit.
I've read dozens of articles about shrimp in the last few months and this is the best picture i have been able to piece together. Please someone correct me if i am wrong.