Probably depends on the birds and situation. I free range most my bids and they show no interest in eating hay, straw, or alfalfa, with the exception of the seed heads. However, if I am keeping in a group for breeding purposes, I do catch a few scarfing down pieces of hay from the runafter they have been cooped up for a few weeks and have picked any grass in the run to death.
That said, I've always used old hay and straw as bedding, and have yet to come across an impacted crop. This is in a span of 10 years and probably a couple hundred birds. However it is a good thing to be aware of in case it does happen. As if it does, you have to act quick if it gets bad.