I'm generally against somebody trying to fake and accent or dialect, but there are instances when it's necessary —— particularly in old blues tunes to make the rhyme scheme work.

I ran into one recently that just jumped out at me. There's a Blind Boy Fuller song (also done by Rev. Gary Davis) called "Mama, Let Me Lay It On You" that has the lines:
I'll buy you a Cadillac car
So you can ride tomar'

I picked up a copy of John Cephus & Phil Wiggins covering the song and John sings:
I'll buy you a Cadillac car
So you can ride to-mo-rrow

and it sounds really weird.

All that said, I still don't like to hear gratuitous use of "dese" and "dat" and "ribba" in singing a lot of the fine old songs that were written that way for use in blackface Vaudeville. Most can be sung straight and still hold up.

david