Yes, we at the regional level get benefits on the mainline partners that we work with. Like Adam said, we are lower in priority than the mainline guys, but we have a lot more options to choose from.
With regards to your main question, most airlines have what is called ZED fare agreements. Basically, you can purchase stand-by travel on a long list of airlines for set segment fees and airport taxes. I have found that this usually works on the long-haul flights. For example, I can fly from JFK to TLV on EL AL for $200, saving me about $500, which is pretty decent. On the other hand, a one-way LHR to TLV on British Airways would cost around $170. A round trip ticket (regular fare, not ZED) would cost about $300-$400. So it is more convenient to fork over a few extra bucks for a confirmed seat.