Malcolm, no. I wondered about that too. He just said, "This quaint word is found in many Irish folk-songs, such as the following:" then gives the example I quoted in my post above.

In my opinion, 'maringo' doesn't seem to be a nonsense word in the context of the shanty - it seems more like a name. 'Skinny-ma-rink-a-doodle' is nearly 'skinny-maringo-doodle' though.