You don't have to claim him but if he meets the tests to be claimed by you, he can't claim himself. SS and Medicare tax withholding is not refundable regardless of who claims or doesn't claim him. The only thing refundable is federal income tax (and possibly state income tax). 

He is not required to file a tax return with less than $6000 of W-2 income. He would get a refund of any federal income tax withheld with income below $6300 if he files a tax return. If he files a return, he must indicate the he can be claimed by someone else (unless for some reason he doesn't meet the tests to be claimed by someone else).

There are certain restrictions for students under age 24 that would prevent him from getting any education tax benefits with less than $6000 of income.