I've just been listening to the Dripkick Murphys version of 'The Fields of Athenry'. Lots of punk electric guitar. Is it folk music?
Is 'Dirty Old Town' by The Pogues folk music? What about 'Fairytale of New York'? When Christy Moore is accompanied by Declan Sinnot on electric guitar, is he being a folk singer?
I asked these questions because Irish traditional music and singing has always thrived on absorbing other traditions in a creative manner: bagpipes into uilleann pipes, the bouzouke, the quadrille into set dancing, Gregorian chant into sean nos ... and so on.
On this basis, celtic rock would seem to me to be a natural continuation of the Irish tradition.