Iowamom, sorry to hear about your son's PC.
There is certainly some truth to your take - pitching can break down arms, particularly those with bad mechanics and/or throw very hard. But, given the context (training company does video analysis of pitchers), I would certainly follow up. Get as much detail as you can from that trainer as to what the specific problem is. What motion does he consider risky and what adjustment is he recommending. Do research. Introduce the information to those who are currently working with your son and his pitching and/or throwing motion. I suspect that if you bounce this off enough good baseball people, your son will either make a healthy adjustment or come to peace with his current mechanics. It would be best to bring this up with people who your son is working with in person but it wouldn't hurt to include this HSBBW group with the details. Lots of pitching and trainer types here.