In the 1870's, if I read Land Where the Blues Began correctly, the African-American railroad worker held a prestigious position within his culture."Babe when you marry, marry a railroad man.
Everyday a Sunday dollar in your hand."
If we take this, then John Henry would already be somewhat of a hero in his community. And John's job would be the source of his standing. In that sense, John would be loyal to his employer, no matter how oppressive, because the employer was the source of John's status and perhaps his self-definition. If I remember my sociology correctly this is a common situation for both slave and worker. In this manner, the song is reflective of the culture from which it has arisen.
I think it is more significant that this song is beloved by African- and European- Americans for the overcoming of the mechanical drill (read industrialism, progress, etc.). It endures as a folk song, because the folk identify with the oppression of modernization and the belittlement of the work of a man or woman.
Roger in Baltimore