I've been reading Forrest biographies since I was in high school and don't know where this comes from. I can assure you that Wyeth in That Devil Forrest never says a word about Black Confederates under the great Confederate leader's command. I have read and reread that book too many times to have overlooked that.
Aside from the escort company supposedly having a large contingent of black members, it was not a group of picked men from other commands. Capt. Jackson's company was recruited from Lincoln County TN specifically as General Forrest's escort. The rolls are available for anyone to see, and how it's been determined that sixty-five members were black, I don't know.
I'm open to suggestions.