Mikefule...I guess I generalize because there may be more "folk harmonica" players here in the US..I have heard a number of them. Ralph Lee Smith is one of the better examples, and Saul Broudy (used to play with Utah Phillips but does solo stuff also) is amazing...and occasional poster here "Songbob" plays harmonica a lot...when he isn't playing guitar, mandolin or banjo. Add to those a LOT of black blues players, and I've heard quite a variety....including the totally amazing "Harmonica Frank" Floyd, who was the 'Spike Jones' of the harmonica. (I wonder if he is still alive? He was not a young man when I heard him 25-28 years ago.)

Having read your comment that "There are significant differences in context and motive between folk and non-folk.", I think we agree on almost everything except a personal notion of the relevance of terms like 'traditional'. ;>)