Just between the two of us, I doubt most of those 113 even know what giveaway they entered... :) No matter how useless the giveaway, no matter how bad the game, people (or their giveaway entering script...) will always try to win it... :)

For the collectors this GA is very good because you can receive uniqe item (especialy because game was shoutdown). So you should judge other by only your point of view, i think ;)

Hmm, I don't know. Unless something strange has been done by the publisher, keys for this DLC should work fine. Generally, removed-from-the-store or purchase-disabled game keys will activate the same as any other keys. You might not be able to play a multiplayer game if the servers are shut down, but it would still be in your library so you could idle it or take screenshots of the menus or whatever. Unfortunately I'm not an expert in removed game stuff so anything I'd say about this specific dlc would just be a guess...

I seem to remember reading that you can check something on https://steamdb.info/ for those rare occasions where a publisher has not allowed people to redeem perfectly good keys, but I don't know what you'd be looking for. :( Apparently it's very uncommon for anyone to do that, but it has been done once or twice. Also, I don't remember where I read about it so I can't give you any specifics, sorry... :)