No, I don't think so. Bartok made his career off of Hungarian folk music, and he's one of the most respected 20th century composers. Come to think of it, it's hard to think of a composer that wasn't inspired at least a little by folk music. I guess later in the 20th century - after WWII, you see less and less of that.
But anyway, I think Janacek has more credibilty than you give him credit for. The average Joe on the street has probably not heard of him, but he isn't thought of as a hack in the academic community or anything.