I'm not suggesting for a moment that you should take this on. It's entirely on goodwill that you've done what you have. I'm really just throwing out ideas, because for some reason I got thinking about the best way to do giveaways. Just seems that if the giveaways are to continue, maybe there's some value in making it a really easy task to take on.
With regard to your first paragraph, the way I look at is if there's some code running on the page, and some database interaction, there is conceivably some way to mess about with what's returned. I'm just saying, if we assume things have been compromised, there's only a limited number of ways you could try to influence the result (duplicate entries, submissions from non-eligible users), which could be double-checked quite easily at the point of closing submissions.