This has nothing to do with the beta. I got a couple dozen of these and never applied for the beta. I get one or two per week for WoW and Diablo III.
Most likely it's what someone else said. RMT after lucrative legacy/beta accounts. They're using FFXI because more people play that so it's a wider audience, and since XI and XIV accounts are linked to SE member accounts they can hit two birds with one stone.