I think the tune is the same as the Sinking of the Fanad which is in Sam Henry's book of old Irish songs.
Catspaw made a point about songs making heroes out of men who were " operating in an unsafe manner and against regulations".
Listening to Missippi John Hurt's version of Casey Jones I get the impression that the song may be mocking the "noble engineer"- especially in Mrs Casey's rather callous reponse to her husband's death :
When Mrs Casey ,when she got the news
She was sitin' in the kitchen lacin' up her shoes
G'wan little children, g'wan she said
Go on into town see if your daddy's dead
Mamma oh mama , how can it be
My daddy he got killed out on the ol' IC
Hush little children , hush she said
We gonna draw pension now your daddy's dead.