Teaching Elder,
In my experience,. everything I've read and my pitching sons have been taught it is about strength in the lower body & core and flexibility in the upper half of the body for pitchers. The only upper body exercises I recall college son telling me about were band related for acceleration and decceration. So, if he is using bands today, stick with them. Ptiching is about timing and getting that whip action (flexibility) in the arm. FWIW - I truly believe this approach as I've adopted some of my son's former college baseball exercises into my own life (tennis) that have kept me out of the Dr's office at 54 years old. I can still bring the heat! ;-)
If this is something you are strongly considering, I would suggest speaking to a pitching professional who has experience in these matters. Pitching is a violent motion, but I think there are things that pitchers can do to help themselves stay in the lineup.
As always, JMO.