We will be able to activate the key regardless of what we have. However, some people prefer to give their keys to people who don't have the base game, so it goes to new hands. Other go along the rules and tell people to not enter if they have more than half of the bundle. Once again, rules say that in the end, it's the giveaway maker's decision.

This case is a common case; the base game was given away for free and most people don't have anything else (2 free DLCs IIRC). So what we are asking is not if we're able to e.g. activate the key if we win; we're asking if you allow people with base game to enter, instead of entering and then you opening a ticket to reroll for a new winner because the original winner has the base game (making people waste points, and support waste time). That's why in bundle giveaways there's always someone asking politely if we are allowed to enter for DLC only.

There are DLC bundles without any base game (which you should have to activate the key). In those cases most giveaway makers ask to either don't enter if owning any DLC, enter only if owning less than half the bundle, or only enter if not owning anything. Just the same options as a bundle with a game; but it's more common to allow to enter even owning base game, due to what I said: there are many people who only have the base game because it was in a free promotion once, but have zero DLCs, and often the DLCs are more expensive than the base game.

I hope this clears things. If you still have any doubt, ask away, we're here to help.