You act like MNF takes up a lot of his time. Other than for the production meeting with the coaches and players, a few hours of studying tape, and maybe going to see a practice, there isn't much more to his broadcasting job. One of the arguments people used for why he wouldn't take the Tennessee job was because of how little he worked right now and how much money he's paid for such little work.
If Kirby Smart could balance preparing for the national title game his final year at Alabama along with recruiting for Georgia, I'm sure Gruden could balance calling MNF games while recruiting for Tennessee.
Plus think of how this helps recruiting. Having the head coach of the Tennessee Volunteers football team calling Monday Night Football for the next 5 weeks is incredible free publicity for our program and should help when it comes to recruiting kids in the 2019 and 2020 classes. They probably watch the NFL more than they do college cause that is where they ultimately want to be. It would be great for us in recruiting if Gruden is calling Monday Night Football games while officially the head football coach at Tennessee.