There are 5 conditions which must be met for a persons (his parents) to claim him as a dependent.
If they don't meet all 5 they can't and the answer to the question in the OP is "No".
If his parents (or any other person) meet all 5 criteria he should mark "Yes".
http://www.taxesindepth.com/info-tax-exemptions.htmlSo IF and ONLY IF all 5 conditions are met should he mark Yes, he doesn't claim himself and his parent claim him.
Now that being said the IRS doesn't really care unless TWO returns claim the same person. Tehcnically the reason the question is "CAN" if that if the 5 conditions apply he has no choice he must market "Yes", not claim himself and his parents claim him. That being said in the real world the IRS doesn't care. It would be far too complicated to verify each claim to make sure the right person is claimed on the right return. They just look to match that no person is claimed twice.
That being said. If he and his parents decide not to talk and they both claim him, 100% guaranteed he will be audited. When he is IF his parent "CAN" claim him, then they are right and he is in the wrong.
One last point. Almost always it is more beneficial for his parent to claim him. They likely have higher income and higher marginal tax rate so net-net there is a greater benefit in parents claiming him.
Simple answer:
1) He should talk to parents
2) Make sure both entities don't BOTH claim.
3) Make sure they don't NEITHER claim (leaves money on the table).
4) Almost always it is better for parents to take the exemption than the child.