The Song:In order for it to be more authentic, Beck filled out his
Song Reader book with additional fragments of songs and melodies, as well as fictional album collections and song titles.
Ye Midnight Stars is one of those, a collection of "songs from the afterlife." All the titles listed, including "Who Is It? Oh, It's Death" are humorous, gospel-flavored, and referring to death, heaven, hell, etc.
I don't believe it references anything in particular, though there is a famous bluegrass song by Ralph Stanley called "O Death."