I wasn't aware that there was a "Southern style" of spelling.
I do recall reading that, before the Revolution, plantation owners were more likely to send their sons to be educated in England than wealthy Northerners. The South did maintain stronger relations with England, even after Independence, and plantation owners saw themselves as the equivalent of the English landed gentry; so the idea that they affected English styles isn't unlikely.
But, that's just the upper classes. I don't think my hillbilly ancestors used English spellings or any other spellings as most of them were illiterate.
I also recall from a Southern history class I took in high school back in the stone age, reading the observation of a Northerner that plantation owners' sons spoke in a refined manner like English aristocrats,but the daughters spoke like the slave women. This was attributed to the fact that boys received formal educations but the girls were raised by household slaves.