The voucher T&Cs say -'The person named on this voucher is entitled to....'
They don't say 'The person who paid APD is entitled to...'
Having said that they do say This voucher is non-transferable and is valid only for travel by the person named on the front of the voucher.
I assume that the original intention was that the pax name should have been written onto the voucher at time of issue, thereby making this question a moot point.
I would also assume that Virgin cross reference voucher entitlement when they receive it. When I used one of mine, I had to send it Recorded Delivery to VS and my Eticket wasn't issued until they received it. I am guessing that once they had the voucher, they checked I was entitled to use it and issued my ticket. I can't be sure of this though.
Nick