jbbaseball,
First all, I truly wish for the best for your son.
It sounds to me like you are doing all the right things.
Getting the right information and getting the second opinion is exactly the right approach.
Taking a portion of your post, the rehab of no throwing for 6 months isn't anything I have heard/read about or experienced with our son. The ability to begin throwing post surgery is an estimate based on range of motion and strength, and medical oversight.
The more normal time to begin throwing is 3-4 months with good recovery/PT and strengthening. The throwing rehab program itself is 8-12 weeks, also if all goes well.
With regard to the "playing cannot make it worse," I can tell you our son did hear that. Personally, I have my doubts.
As you know, a MIF is going to be making throws from various positions, many of them off balance. He will also be diving for balls with his arm extended.
While it may or may not be true that "throwing" alone won't make it worse, that isn't baseball the way our son's play it.
In effect, playing this season is a question of how much pain your son can endure and the extent of clicking/catching/instability he may experience.
Playing with a labral tear is as much mental as it is physical. You need to know that in advance.
In my view, it also requires a coach who truly can help deal with both and who can help your son fundamentally in the field so that he, to the extent possible, he reduces the stress on his shoulder. I cannot underestimate for you the mental component of this situation.
With all that said, it is very difficult having your son assured that "playing won't make it worse" and hearing, after the surgery, "that was worse than the MRI showed."
As you might be able to tell, we have some experience and our son is a MIF.
Please don't hesitate to PM if you would like to discuss more privately.
I am really hoping for the best for your son.
He is lucky to have your helping him.