I'm with Jim Dixon. Accents or dialect may be an affectation for a performer, or they may be perfectly comfortable with them. A folksinger is often singing a song the way he or she learned it, un- or pre- consciously, and the notion of 'performance' becomes peripheral to the communication. And anyone who ever heard Frank Warner sing understood that he WAS for the moment the person from whom he had learned the song, and that he was bringing whole the experience and history of that person. The nature of the dialect was simply not separable from the song. A singer-songwriter from the suburbs may find grammar an issue of sincerity of presentation. Not the same problem!