The question is whether you can use
the DLC without an internet connection. Can you play, say, the prequel adventure Lelianna's Song without an internet connection?
Because the ERF archive files, the ones that contain all the assets for the DLC, in Addins/dao_prc_lel/core/data are encrypted. In fact, they're completely identical with the Steam release. How this usually works is that the game contacts the BioWare servers, tell it "Here, I'm CD Key blablablah", then the BioWare server sees that it's the ultimate edition and is authorized to use this DLC and it gives the game the password to decrypt the ERF archive.
If the GOG release does not contact the BioWare servers, it still needs to know the decryption keys for the ERF archives. Those would be stored somewhere in the game date or the EXE file or something. Can someone confirm that this is the case?
Because otherwise, if it still contacts the BioWare servers for the decryption keys, I'm not sure you can really call it DRM-free...
I think they are pre-activated. So no connection is happening. You can unplug your internet cable and still play everything. Thats what I understood from the blue messages.