Jiggaboo (so spelled) in print in 1926, Finerty, "Criminalese." "A Negro or yellow race chauffeur. Lighter, "Historical Dictionary of American Slang." Sometimes spelled zigaboo. Jigaboo is in Mencken, "The American Language." Probably older than the quote in Lighter.

See "I've Got Rings on My Fingers," sheet music, 1909, with "Mumbo jumbo jijjiboo," but Lighter questions the connection.

Never heard jigaboo used for a ghost or ghost story (post by meself) but I wouldn't doubt it. I doubt the connection of the derogatory use with bugaboo.