Never mind, just asked to the support center and they confirmed your answer
Thank you

This of course changes if there is some kind of GOG key exchange from Slitherine purchases, but that is outside my area of expertise. Well, in the multiplayer login screen I see a serial key but I cannot register the game in the Slitherine site with it. Maybe I must post the query on another sectio...

Hello,
I have purchased Sanctus Reach from GOG, can I purchase the DLC from the Slitherine site? Will they work with the GOG version of Santctus Reach?
Thank you