Putting in strange spellings to try to show how the accent sounded was a convention of the time. William Barnes did it in his Dorset poems. Kipling did it in Barrack Room Ballads. George Orwell commented how it often got in the way of really listening to the words.

Sometimes it's accurate enough - people do often pronounce "the" as "de" in many accents - but it doesn't really help writing it down. Spell it out in standard spelling, and read it with the accent in mind, and it's likely to be far more accurate anyways.

I suppose sometimes it was done as a way of making fun of people, but I suspect very often it would have been meant with the idea of reespecting the way people actually spoke. There's nothing any funnier about "de" then "the".

Change to orthodox spelling here and there's nothing disrespectfiul about this, aside arguably from "darkies". Apart from disrespect to the Master legging it:

Say, darkies have you seen the Master,
With the moustache on his face;
Going along the road sometime this mornin',
Like he gonna leave the place?
He seen the smoke 'way up the river,
Where the Lincoln gunboats lay,
He took off his hat and left very sudden,
And I expect he's run away."