I'm under the same impression regarding Dobbins. I've read through all of his letters housed at the University of Arkansas, and my impression has been that the war really took its toll on him physically and mentally. Although largely conjecture, it appears that him and his wife had grown far apart by the war's end, and Dobbins became something of a wanderer. I've studied the cases of many men who went to Latin America following the war, but most returned to the states or remained in Southern enclaves, Dobbins on the other hand really seems to have abandoned his old life and "changed his identity" as you noted. Its really fascinating; I only hope that in time more about his experiences in Brazil reveals itself.
Matt