Genge did that certainly.
That scrum was pretty unsteady to start with - that the ref had gone to that side suggested he thought that was the side most likely to be where there wold be trouble.
Couldn't say about consistency as I've not seen any discussion, I think sometimes it depends on when in the procedure it happens.
It's quite strange - for a few years the scrum was depowered and there was a vogue for running props. Recently, it's come back to prominence and you need scrummaging props instead of runners. I'm not sure SA ever indulged in the idea that a prop's job was to do anything resembling running!