I used distribution from a 529 plan (to pay for off campus housing = amt. for a dorm room.) for my beneficiary. Can he claim on his tax return if he is not my dependent?

[tn1]

Is the rent off campus housing eligible  if it is not owned by the college?

[Hal_Al]

No.  But you can claim it, as long as he is the beneficiary of  the 529 plan that you are the owner of. He does not need to be your dependent for the distribution to be qualified for the earnings exclusion. 

For 529 plans, there is an “owner” (usually the parent), and a “beneficiary” (usually the student dependent, but it doen't have to be). The "recipient" of the distribution can be either the owner or the beneficiary depending on who the money was sent to. When the money goes directly from the Qualified Tuition Plan (QTP) to the school, the student is the "recipient". The distribution will be reported on IRS form 1099-Q. 
The 1099-Q gets reported on the recipient's return.** The recipient's name & SS# will be on the 1099-Q.

You are correct, off campus housing cost is limited to the amt. for a dorm room, for the deduction.

**Alternatively; you can just not report the 1099-Q, at all, if your student-beneficiary has sufficient educational expenses, including room & board (even if he lives off campus) to cover the distribution.  

[Carl]

if he is not my dependent?

What makes the student not your dependent? I ask, because it is rare for an undergraduate to not qualify as a dependent of one or more of the parents.

Basically, the 1099-Q is reported on the tax return where the named beneficiary recipient on the 1099-Q is also listed "somewhere" on the tax return' either as the tax filer or as a dependent.  So if the student is your dependent, that means the student's SSN is on your tax return. Therefore you can claim it. If the student will be filing their own tax return, then the student could claim/report that 1099-Q instead.