One thing to understand is that Kevin O'Sullivan (a/k/a "Sully"), who was their chief recruiting assistant for years (also the pitching coach), took the head job at U. of Florida 2 years ago. So any experiences going back more than a couple of years may not be as enlightening as you would like.
That being said:
We attended a camp there in fall 2006. Probably 600 kids there. Through the course of the camp, the coaches pulled 6-8 guys aside and indicated they'd like to spend more time with them. These guys got a tour of the team facilities and were followed up with more individually by e-mails after the camp.
We've also known kids to get identified and targeted through the other standard channels -- a tip from a scout, a contact from a respected high school coach, scouting at WWBA and showcase events, etc.
If your son has good grades, one advantage Clemson offers is that an out-of-state kid can get the in-state tuition break if he finishes in the top 10% of his HS class. Not quite as good as the in-state breaks available to good students in FL, GA or TX, but something to consider.