I think songs are spiritual things and great old songs have a spiritual "essence" that enables them to survive and travel down through the years. The really powerful ones can last hundreds years and some go so far back into the misty realms of antiquity that no one can really sure where or whence they originated. Singers too have an essence and when singer meets song the two essences blend and something unique emerges and sometimes it works or maybe not. The best singers seem to be vehicles who try to channel the song and try not to overthink it as far as delivery goes. If a song speaks to you then just sing it and see what happens. Maybe it's essence will harmonize well with yours. The idea that one must be from a specific region to sing a particular song is just provincial, plodding, pedantic, school-marm thinking. The bloody Beatles all spoke with British accents and sang with American accents and it seemed to work out fine. All the greatest artists have always been iconclasts who loved to shake it up. Elvis Presley created rock and roll when he mixed white hillbilly music with black rythmn & blues. Johnny Winter, a great blues singer, is whiter than the driven snow. I just read a book about Robert Johnson that claims Johnson and all the other bluesmen played all sorts of stuff, tin pan alley, broadway showtunes, cowboy songs, scottish & welch ballads, irish sea chanties, etc, and it was the white record executives that forced them to focus on the "blues" tunes in their repetoire. Some of the best country singers in America are not from the south but from places far north like Canada. So in short I say if the shoe fits wear it.