In terms of technical training probably not a right lot. Rugby players do use the pads quite a lot in warm ups/warm downs.... The current HW division only requires someone to be in decent shape and to be able to whack a bit and you'll generate a bit of interest.
I am 6' 4" 280lbs Rugby player, who has smashed my fair few opponents, and taken my licks. But when I tried the amatuer game, I was an uncoordinated bumbling fool, without a hope. Boxers, even top class Heavyweights of this era, are very classy athletes, I seriously doubt a Rugby player could crack the top 200, let alone be anything approaching world class...
I don't think he'll be anything approaching world class, partly because he's clearly not good enough and partly because it's only a part time job for him. He can smack around a few heavyweights that are officially classed as professional boxers though.