Well, Fat Possum is definitely a blues label, and they have good reason not to promote themselves as "folk." Whether you consider the blues to be "folk" or not is up to you and the people you associate with, and either position could be anaethema to one group or another.

That is, some blues lovers hate what they perceive to be "folk music" and don't want to be associated with it. And some other folks who love folk music including the blues have the exact opposite opinion.

The Fat Possum artists are all pretty forthright and unpolished. For my money, that makes 'em folk-blues, which is about the highest compliment from me.