Same thought... actually, I never fully understood the idea of committing to a D3 school where you are not academically accepted yet.
The wise advice always given here is to keep the foot on the pedal until there is a reasonable level of certainty (even then, keep doors and communication lines open). Your description of his status is far from that...
"... this is one of those schools that does not have "slots" for athletes. He has to get past admissions, and the school is extremely selective. I don't believe the coaches would have recruited him if he didn't have a chance, but it's far from a sure thing. His pre-read was not a slam dunk, but also not a "no"."
It shouldn't be any problem to attend the event under those circumstances.