'Correct' grammar is actually 'standardised' grammar. At one time a country like Britain had dozens (possibly hundreds?) of different dialects. These dialects were variants of English, each with its own vocabulary and grammar. My maternal grandparents were born in East Anglia but, soon after they were married, moved 50 miles further west to an East Midlands city in which my mother was born. My mother had great difficulty understanding her own grandfather because he still spoke his local dialect.

Standardised grammar is an invention of human beings designed to improve communication between them (or to assert the dominance of particular social groups - depending on your point of view!). Deliberately subverting the rules of standardised grammar for artistic purposes is not 'wrong' because those rules are arbitrary anyway. I suppose the key question is does the subversion lead to an improved artistic experience for the audience?
As for singing in a dialect different from your own, well, it all depends whether or not you can do it convincingly ...