I heard it was made by Daniel Decatur Emmet and that it was spread along with blackface. Is this true?
Emmet was blackface minstrel performer from Ohio, and the tune was often sung by blackface minstrels- and minstrel shows lasted into the 1950's, so that was likely a lot of people singing "Dixie". It was sung by a lot of others: even though it became a Southern anthem, Lincoln liked it as well ( p.172). It was a catchy tune that sits well on the banjo, and the basic lyrics are not particularly offensive, joining a zillion other songs about how much somebody loves their home. A good tune is a good tune, and like many good tunes ( like with medieval contrafacta) other words were composed for it."Dixie " got various parodies created during the Civil War by the Union, sometimes with nonsense lyrics, and had fiercely aggressive ones created by Confederates. All of them took advantage of the fact that it could sung while marching and had a good chorus. My favorite parody I have been unable to track down- it my be Civil War or it may be recent-
I stuck my foot in a ground hog hole And the ground hog said Lord bless my soul Take it, take it out, Reeeeeee-move it.
Emmet was not the only Northerner to write tunes about the South: Stephen Foster was born in Pennsylvania and died in New York City, and also wrote songs set in the South , for the minstrel show world- and yet some of his songs were good enough to rise above that: it's rare now to hear his once popular "Camptown Races", but you can still hear singers doing "Hard Times Come Again No More" ( a real gem) and "Angeline Baker" is a very common fiddle tune in the Old Time/Appalachian repertoire. And Kentucky had no problem making his "My Old Kentucky Home" their state song, even though he likely never went there.
You can also place Emmet into the huge group of professional songwriters who have simply identified a genre and written for it. "Danny Boy" was written by Englishman Frederick Weatherly, using a traditional Irish tune, and yet most people now think of it as a traditional Irish song. Various comic Irish-genre song hits of the early 20th c., like Who Threw the Overalls in Mrs O'Murphy's Chowder were written by Tin Pan Alley songwriters in New York City, who were often themselves Jewish and had never even seen Ireland.