My very good doer had haylage all last winter, couldn't get hay. I just tried to slow her down eating it, tricklenet or double netting. Mind you she had zero grass pretty much. She came out of Winter a similar weight as she went in and she loved the haylage. You can soak it but insure how long it would need soaking to remove sugars.
Hm I am interested in this, as my new yard only supplies haylage so not sure whether or not to order in some hay or to try the haylage first. I have a good doer who will be in at night. I use minimum rugs and no hard feed but even on that, last year he didn't shed any weight with soaked hay.
We have to feed haylage, as we can't get good quality hay. We feed a relatively small amount and supplement it with oat straw chaff (Honeychop), so that they are not standing in with nothing to eat.