Q,
Good job with the walkaround.
You are asking an important question, the extent of "authentic" black content in minstrelsy. It's one of the main questions that is entirely open to answer even still. Rourke felt the walkaround had a resemblance to black performance traditions. Later scholars are still trying to get a grip on the origins, not to mention purposes and impact, of minstrelsy.
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Lighter makes a great point, that songs change in their meanings and resonances over time. This is definitely true of "Dixie." It's still a difficult song to perform, for its complex associations, and in fact, the little community festival here --the Dan Emmett Music and Arts Festival, which we founded in 1980 (but no longer are associated with)--for a while banned the singing of "Dixie."