Stackolee was based on a man whose last name was Lee, and whose nickname was Stag or Stack. The book Stagolee Shot Billy makes that abundantly clear. It documents the fight (which took place in St. Louis, not Memphis or New Orleans) and the case at good length. At the same time, there was a Mississippi riverboat called Stack o lee which I believe was owned by another Lee family, though I forget the details. That's how Stag Lee became Stackolee to people who didn't know him.

There's little room in there for a West African demon, but West African Aesthetics may inform the structure of the Blues Ballads about Stackolee, as many of them resemble praise songs (vignettes about a powerful man, and his qualities described, not in any particular order) rather than Euro-American ballads (linear narrative). This is speculative, but some scholars have made this argument about African America Badman and Hero ballads generally.

One thing that did happen was that characters like Stackolee and Railroad Bill were ascribed supernatural powers. This can be traced to the African American magical tradition of Hoodoo, which does go back to African (Yoruba and Congo) roots. So some characteristics associated with West African supernatural powers may have crept into the story sometimes. I'd recommend John Roberts's book From Trickster to Badman on this. (That's John Roberts the African-American folklorist and past president of the American Folklore Society, not John Roberts the English Folksinger!)