I get a bit tired of the "You're a Folk Singer - why are you singing non-folk songs?" attitude of some people. Didn't Louis Armstong say, in answer to the "Is it folk music" question, something on the lines of "Well! I ain't ever heard a cow sing..."
As far as I am concerned, singing is singing and music is music. Norma waterson has certainly been known to say something to that effect. As far as I am concerned it has more to do with style of performance than who wrote it.
Jazz singers and bands happily take ANY song or tune, jazz it up, and it automatically becomes a jazz number.
Scots and Geordies take ANY song, change the words to the local dialect variant and it immediately becomes THEIR song.
The Irish just claim ANY song written ANYWHERE as an Irish song.

When Van Morrisson records with the Chieftains, does it make HIM a folk performer or does it make the Paddy Moloney a rock star?

Some of my personal inputs are "One big thing" originally performed by Scottish rock guitar band Big Country, which is an uplifting song I do unaccompanied. Another is Purple Haze done with clawhammer banjo - well Hendrix MUST be a folk singer because he did Bob Dylan's All Along The Watchtower...

The reason I don't do much Rhythm and Blues is because it doesn't sit well on the banjo, not because I don't rate the songs.
Quack!
GtD.