At first they were blocked by a patched called “DLC blocker” now they are pre blocked but the GOG installer. I know this can be undone by editing the gog.ini file but I’d like to ask that you go back to using the patch instead. It might be unbalancing but it is the way the game is meant to be played.
I've sent this message to GOG support as well, but I'd also like to know what you guys think. I am one of those people who like the bloodsucker and unlockables pack. It's great for a second play through. Also the unlockables pack grants you everything so you don't have to worry about missing out on something because you made the wrong decision during a mission.