Hi, there isn't any DRM, early players misunderstood how bounty/treasure keys worked. The Multiplayer part of the game requires you to login with a unique name and there is a registration. The DLCs in question are free and included with the game. Hope that helps.

Bounties/Treasure hunts are an end-game content of randomly generated objectives which drop to players.

They have an expiration of 1 week in which they could be completed and can be given to other players, too. You can share them directly in the multiplayer chat with a unique code. Most people also use this discussion here. - Steam Discussion for sharing codes

So, they can drop to you in single player. But if you want to use a code from another person which dropped to them - you'll have to connect to the server to verify that it's a legit code and it'll send you the objective.

The early players raged about a similar code which we gave away as a reward ONLY to GOG players. It wasn't anything special that a player would miss, just some gold and 2-3 starting items. But they didn't like that they needed to register and go online, so that the code could be redeemed. Then we patched it and the reward from the code just drops on the ground after you finish the tutorial and select your diffuculty/outfit.

:)

Yes, you can. Also the thing with the firewall was resolved in the latest update. It was all along a problem with the galaxy api. The linux version is lagging a bit behind on that fix, since it has some issues and is not pushed live for the moment.