I don't think anyone would say that he's not accomplished and yes I do have a Martin Simpson album or two.
However, I don't expect anyone in the folk sessions around here would consider the piece he's playing "Folk" in the sense of the word.
That said, it's the only piece I've heard him play as such and therefore it may not be representative.
Like big Al says, technically he plays guitar quite well and obviously through a fair bit of practice.
I still found it quite boring to listen to though.