I reckon a lot of the bannocks made in the past used barley rather than oats. It's just not available in the shops. I just checked Amazon...its over £5 a kg.
"Any history of it being used that way?"
I reckon it was. Poor people are omnivorous and creative: they can't afford to be otherwise.
I do have a 17th c Scottish recipe book somewhere about so I shall have to check. The same book gave me one of my favourite dishes which was leg of lamb seasoned with anchovies and wine...oh yum.... something I didn't see again until the much underrated Keith Floyd.
On oats I do remember the exchange between the conceited Samuel Johnson and Boswell, who was otherwise something of a sycophant:
Johnson: "In England we wouldn't think of eating oats. We only feed them to Horses."
Boswell: "Well, maybe that's why in England you have better horses and in Scotland we have better men..."