re: How does the OL know whether to run or pass block in this RPO scheme?

I doubt that refs pay attention if the block begins within 1 yard of line of scrimmage and block is held while pushing defender beyond the 3 yard mark. If on a LB setting back and moving laterally big difference.

It used to be that a blocker if maintained their block could push downfield as far as they wanted. That is not the easiest thing to do for any blocker.