If I recall correctly, a few years ago PHX was using Express runners plane side to download connect bags going to Express flights. I guess they did such a lousy job that Management decided to use mainline runners instead, so I am not sure there is much which violated the CBA, as it was once common practice in PHX.
Someone who was once in LAS told me that he would run the United interline bags which were part of the STAR alliance. UA ramp agents would leave them on the side near the belt loader, he would pick them up.