As a complete non expert, I seriously doubt they would be running the replacement engine. Would make the whole job significantly harder. Given the damage done, to hang an engine you are principally looking at a metal bashing exercise.
To get it to run, you would need to make sure the fuel, hydraulics, air, and electrical/electronics are safe and functional.
This would be a lot more work.
Given that there is a significant amount of damage, it would (I would have thought) be much safer to isolate these supplies, and just use the engine as a known amount of ballast, with known aerodynamic properties.