UA did protect me on DL GSO-ORD of their own accord (I am a 1P), but unfortunately didn't bother to let me know so I checked-in for my UA flight after the DL one had departed, resulting in a six-hour weather layover at GSO for ORD to open and my UA flight to depart.

So they can do it, but it's probably up to the agent's/airline's discretion to do so.