Sultan apparently was suffering the effects of too much corn juice when he related the unrelated in his post.
"Cracker" was defined in print at least as early as 1766 (see Mathews, Dictionary of Americanisms, the quotation in the "Historical Dictionary of American Slang," vol. 1, J. E. Lighter, pp. 503-504:
"I should explain to your Lordship what is meant by Crackers, a name they have got from being great boasters; they are a lawless set of rascals on the frontiers of Virginia, Maryland, the Carolinas, and Georgia, who often hange their places of abode."
In 1772, McWhiney, "Cracker Culture," wrote: "The people I refer to are really what you and I understand by 'Crackers' - persons who have no settled habitation and live by hunting and plundering the industrious Settlers."
In the 20th century, the meaning had changed.
1908, Sullivan, in "Criminal Slang"- Cracker: a poor Southerner.
By 1924, the term had become perjorative in a racial sense- Clarke, "American Negro Stories," They's a thousand shines in Harlem would change places with you in a minute jess f' the honor of killin' a cracker." The term had evolved in Black English (esp. in urban areas of the north) to mean a white racist (or just a white
Southerner).
I will agree that the name "Atlanta Black Crackers," was 'cool,' a nice twist.
By the 1920s in white Georgia, however, the appellation Cracker was on its way to respectability, with some Georgians referring to themselves as Crackers.
In Florida, if the term is used as a racial perjorative, it is a violation under the Florida Hate Crimes Act.

Crack corn- referring to corn whiskey. This possibility is referred to in several early posts to this thread. In the song, it showed up between revisions to the song between 1846-1848 (see post above by rich r) in Minstrel Shows, and also possible could mean cracking wise, but the former is more likely. Richie, in another thread, noted that cracking corn also was a slang term for snoring or sleeping.