I do not think the site has the right to reveal the identity of this person. Most sites will display usernames, but I still have doubts if this is allowed.
Suppose someone his name is "Mike Michaels" and choose his username "Mikemichaels", then I can imagine he will not be to happy to display this name as a winner.
Now is Mike Michaels a made up name, but I can imagine there are people with unique names, that is really a privacy problem.