Cadaver747: By not having Origin running. I mentioned above that there were no issues on my side. And since when Origin scans GOG game folder?
Could anyone confirm that Origin *latches* onto its games from GOG?
NuffCatnip: That 'latching onto' part is completely false (from my limited experiences/point of view).
I've played gog games from EA while running Origin, hell I ran Saboteur and Dragon Age Origins on Origin and right after the gog version and then the Origin version again without issues. I don't know if there'd be any save file location issues, but running the games wasn't an issue.
I don't own Dead Space on Origin, but I can't imagine that it behaves in a different fashion.
Edit: I don't use galaxy, only the offline installers.
You need to have Dead Space on your Origins account. After you boot it up and have automatic updates on it takes Dead Space into it's infrastructure and downloads additional data do be dependant on it.