With all the bulk run-through trains the carriers are handling - oil, grain, ore, coal, ethanol that run interline routes you are likely to see any carriers power on any other carriers lines at any time.
With the crush of business that all carriers are facing - any engine will do when it comes time to run a train - your power, foreign power - any power.
I saw a single NS leader on CSX's Q197 a few months ago. I think the train runs from Nashville to Savannah via the CSX Georgia Subdivision with a stop at Hulsey yard. I think it's the first time Ive seen NS power on the CSX Georgia Sub.