This worked great for my son, who was a pitcher. There were a handful of returning players there for summer school, and they worked out a schedule for working out on their own; on the field/bullpen and in the weight room. The team's coaches could not be involved until the regular academic year began, but the strength and conditioning coach could be.
In his case, he started the school year with more credits than he would have, otherwise; and he was in great baseball shape. If he had been a position player, I might have been somewhat less enthusiastic; only because it would have been a challenge to face live pitching in that environment.
Regardless of what course an incoming player follows leading up to Fall Baseball, it ought to be one that puts him there in the best baseball condition possible and rested. The competition of Fall Baseball and beginning of the academic year will tax him physically and emotionally more than he's ever been challenged before.
Best of luck to your son!