I attended many of these camps when I was going through the recruiting process. I was fooled into thinking it would get me seen. Even as one of the best players at these camps I never once got pulled aside to talk or even got a follow up email. My recruiting came down to personal connections and emails. "Prospect" specific camps are a good place to compete, but not necessarily to be seen/recruited. I don't blame the coaches for still targeting your son, but I'm glad you have the sense to not fall into the trap.
If your son has a true dream school, it is worth writing a very strong email expressing his interest in their school/program and even maybe attending a camp in hopes of being seen. If it isn't his dream school, it is not worth it in my opinion.