Same issue here, have the base Blackguards game. Hope it's ok to enter, if not I'll just remove my entry.
I believe I read somewhere (was looking through the FAQ, but things are somewhat all over the place so couldn't find it) that we should just ask the giveaway creator if we can join or not. Basically if a person wins a bundle such as this and he has most of the games, the creator can just ask for a new winner. So basically the creator has the final call.
Don't quote me on this though, because I still haven't found it in the FAQ...

Kept digging and found it in the rules:

What are the rules for entering to win Steam packs if I currently own a number of the games contained within?

• We ask users not to enter giveaways for packages if they already own the majority of the games. This allows for winners that will receive the most value out of their gift. In the end, the giveaway creator has the final say, and if they believe the winner owns too many of the packaged games, we'll allow them to request a new winner.

Sauce from:
http://www.steamgifts.com/about/faq

Roaarr..