Union-wise, I think a lot depends on the area you're in and the type of music you play. I played in a jazz band around Buffalo, NY back in the 70s. We were non-union. We got booked somehow in a club for what might have been a weekly gig. First night went well. Second night there was a union rep in the bar who struck up a conversation with our drummer. Next thing we knew we were on the street. It seems this was a union bar, but nobody in management bothered to ask us if we were union.

Folk-wise, esp regarding trad stuff, I don't think the unions pay us much attention, and couldn't help us much if they wanted to. I think it's more helpful for classical musicians and wedding bands.

But then I may be wrong.