Well, pretty much everyone who has an Apple account has an iCloud account linked to it. You can't turn on Find My iPhone without it.
I'm not clear on whether you have tried going to iCloud.com on a computer and then tried signing into his account using his Apple ID. If you have a linked iCloud account then you can sign in with either the Apple ID email address or with the iCloud email address, so try signing in with the Apple ID.
If you are able to sign into his account on iCloud.com using his Apple ID email and password, then open the Find My iPhone app to see if the iPad is listed there.
If it is, then you can erase the device right from there and then set it up again.
If it is not, then that means that the iPad is locked to a different Apple/iCloud account. At that point, the only thing you would be able to do would be to take the iPad along with the original sales receipt to an Apple Store, and they should be able to remove the lock for you. But they won't do it without the original purchase receipt.
Best,
GB