Not necessarily. If the goal is to make sure that buyers (in private transactions) are not disqualified persons, we can check the buyers without reference to the guns that are to be purchased. The problem is that all the current proposals would run all transactions through FFL's, meaning that a Form 4473 would be filled out, and the gun entered into the dealer's "bound book." (This is a form of registration.) Of course the FFL's love this, because it represents an additional stream of income for them.
An example of a non-registration UBC system is as follows: Let's say you are interested in buying a gun from a private (non-licensee) seller. You go online to a public NICS portal, enter your identifying information, and receive an approval code number good for one transaction. (Perhaps a nominal fee would be charged to your credit card.) You then show the prospective seller the approval code along with your ID. He goes online and verifies that the approval code has in fact been issued to you. The transaction proceeds (or not...) and there is no record of the gun.
The sellers would have an incentive to use this system because, under its terms, they would be sheltered from liability in case the gun is misused. In addition, the ATF would conduct "sting operations" (such as having sham buyers with no approval codes trying to buy guns) to keep everybody honest. (A seller would be fined for selling a gun to somebody without an approval code.)