I know the Soggy Bottom Boys are entirely fictional. They still performed this song. That's final.
The film O Brother Where Art Thou is one of the most visionary films ever created, steeped in myth, history, allegory, symbolism, metaphor, irony, symmetry, dry humor, and MUSIC!!!!!!
The lynchpin of this film is when the pack of Depression-era escaped-con "heroes" of the story take a brief, inexplicable detour in the middle of the action to record a song for a few bucks in a radio station/recording studio on the side of a dusty road. It is a total aberration in the loose plot of the film, a seeming narrative lark - until the unbeknownst mega-fame that their recording gains serves as the deliverance they could neither expect nor even understand until it was upon them. Humans learn fast and take advantage. The entire hustle of music stardom in a split-second decision of survival.
The song is a beaut. There are tons of roots songs as well written and performed. I simply cannot let this one go for the psychic import it carries in this, one of the most spiritually sustaining narratives I've witnessed out of the mountains of films my eyes have seen. And the vocal is excellently delivered by non-George Clooney, whoever he really was. I'm not in a state to care about researching who really sang. It was George Clooney, leader of the Soggy Bottom Boys.