Other than using the emergency lane to get to an accident I don't think so.
Yes, if a tow truck driver is responding to the scene of an accident they can use the shoulder of the road. IT is an emergency lane, who is to say what that emergency is.
It is all in the texas Transportation Code
Look I am not going to do someone else’s homework for them. 35 years driving I have seen it all from driving on the wrong side of the road, crossing the medium, going down a one way the wrong way street and blocking a road way (yes it is illegal) all in the name of recovery. If there is not a law that says it then it is a practice that is overlooked by law enforcement. As far as I know laws that do not pertained to doing a job in a safe manner are not overlooked like speeding and reckless driving
So your statement that driving on the shoulder by a tow truck driver is legal was baseless; therefore, meaningless. And what is a "medium"?