I have done only one drive (or two...there and back) on roads that both had truckies and were single lane. Brissy to St George. West of Dalby I saw truckies indicating right to communicate that it's safe to pass constantly. I had heard about it before and explained it to my co-driver because he was unfamiliar, but this was the first time I experienced it. And my experience was very strongly that yes, it is indeed a real thing.
I have never heard about the left blinker being used in the same way as you describe.