Good question that I am sure will get different answers. In my limited experience, some camps encourage the kids and/or parents to ask the coaches questions, others do not. It certainly helps when the coach approaches you rather than the other way around.
For example I watched my son pitch at a camp and my wife shot video. When he came off the indoor mound and past the netting(due to rain)I gave him a high five for pitching well. A top 10 D1 coach approached me and pulled me aside. I was thinking he liked what he saw and was going to make some type of overture. Instead he said he liked what he saw, and that he knew a coach who was looking for a pitcher like my son. After we talked for a few minutes I asked him if he had any interest, and he candidly said no. He gave me a couple of reasons, first that he had his 2011 class of pitchers already, and that most of the scholarship money was gone. He also said my son did not throw a curveball even once, and that in his conference every recruited pitcher had nasty curves. I pointed out to the coach that my son cut his fingers during warm ups with his bands(broke and cut his fingers in the knuckles)and he could not throw a curve that day. To my surprise the coach said he knew about the injury because there was blood on my kids shirt and he asked what had happened. However he said unless he saw him throw some nasty curves, he would not even consider him regardless of the reason he did not throw it.
At the end of the camp my son approached a couple of coaches from schools he was interested in. Unfortunately neither had seen him pitch, so they could not comment.
However other coaches had seen him and he performed well striking out 8 of the 9 batters he faced. Yet we did not hear a word for a couple of months. I figured since my son did not light up the gun and only threw FB's and change ups, no one was interested. Yet since then he has had a couple of calls asking what he is currently doing, and they want his schedule so they can send someone to watch him. So unless your son is a 90's guy, you never know how long it might take for some of these coaches to contact you, if they do at all.
My suggestion would be for your son to approach the coaches toward the end of the day or event to see if they watched him, and ask what they thought. They might say something insightful even if they are not interested in him for their program. However unless you are solicited about him, I would not go asking as a parent at one of those events unless it is set up for parents to speak directly with the coaches.
Good luck