A hijacking implies that the hijackers are armed - which means that any tugboat attempting to nudge the ship should expect to be fired upon.
Also, @andrewm’s post in the other thread suggests that tugs are privately owned/operated vessels - in other words, like planes at an airport, they may require permission for their activities and might have to follow harbormaster directives to assure overall harbor safety, but I don’t believe they can be ordered into harm’s way; it’d be like a cop ordering nearby civilians to help him end a hostage situation.
Also also, as noted upthread, tugs can’t do a whole hell of a lot to a container ship without its acquiescence, especially if it (the container ship) is already moving forward with significant speed.