We never know who will attend. There is no preregistration for scouts or recruiters. We do know that event has been well scouted in past years. I wish I could be more helpful, but the truth is I can't guarantee that any specific college will be in attendance. No one can, unless they pay the coaches to be there. We don't pay colleges or scouts to attend any event. We want them to show up because they want to be there for reasons other than making money.
I do appreciate your thought process regarding your son and DIII. Velocity below 80 will not impress most DI coaches no matter how good a pitcher might be. On the other hand, it might trip a DIII trigger. There might be better ways to spend your money than attending this event. Please don't take that as an insult. It is not meant that way at all.