Send the documents requested and if the balance is taken from you or anything happens to your account it will be on him.
For what I've seen so far, I don't think he'd be willing to send me the funds so I'd much rather keep my account frozen, than to unlock the account, having negative balance and him not paying which could potentially result in Venmo taking it from my bank maybe?.
So I'd feel much safer if I had the funds first, before unlocking it (I'd obviously refund them if Venmo doesn't ask for the funds)