I think we can tell by the amount of posts a member has (which is easy to check, just by clicking on the name) and how much they contribute to the forum, but I don't think you can punish a lurker who may not contribute but yet gain info.

I think if the votes are really really close, like by 5 votes then I think unknown names need to be checked. If it's a runaway Ride of the Month (which most contests are) then I don't think it needs to be checked.

Also, administrators can check the amount of created usernames in the admin logs in the Admin Control Panel if "prizes" are involved.