If you allow people to enter or not enter for DLCs only is up to you, doesn't go against any rules. Some people don't care about people entering only for DLCs, other say explicitly that they want the whole bundle to go to someone who doesn't have anything.
If you don't specify if people can enter only for DLCs, the winner is considered valid if the account has half or less of the content of the bundle (in this case base game + 3 DLCs iirc).
Note that there are also DLC-only bundles, and also bundles where the base game is cheaper than the accompanying DLC, so it makes more sense to allow everyone. There are also game-only bundles, with the trilogy and such.
Whenever I make a GA for a bundle I try to remember to specify who can enter, e.g. "you can enter if you don't have more than one game in the bundle of three", or "you can't enter if you have any of the two DLCs".
But ultimately the decision is yours, freely. I've not heard of any case where a mod has interferred with the preferences of the GA maker regarding who can enter for a bundle.

The site rules say "The gifter decide if he let reroll if someone have something/the majority (in worth or number, as far as i know) from a bundle/special edition", so Lugum questioned in the end if you would allow a winner that have the base game (entering for the DLC's) or if you would reroll that winner.

It's a friendly way and safe time for the you, the support and the winner because no unexpected rerolls needed.

Thank you.

Entering for expansion too, thanks! :D