I've been hired to do many bluegrass festivals, and they like what I do.They welcome the break. So, I can only conclude that it depends on the performer. I like bluegrass (in small doses) and I love folk. However,I would never do a thiry verse ballad at a bluegrass festival. I've seen many folksingers who put ME to sleep, so it's easy to imagine what someone who is used to hard driving bluegrass would think of them.

Bluegrass is "playing" music" and it's fun to jump in there and get all bruised up, but it's tiresome to just listen to for any length of time.
Someone called folk music, "Heavy Mental".