Having done this myself,question one,no.
Question two,there could be.
Question three,I had to fluff the mulch a bit in the spring,we had heavy rain after snowmelt and I did get some rotting-(of garlic),but it happened in the other bed too,mulched with other material.

Thanks. It seems like a great resource if one lives in dairy country. I am guessing that (to some degree depending on the composition of the haylage) it will provide steady nitrogen perhaps eliminating the need to sidedress with bloodmeal.