Thanks, I may contact them too.
Yup, it can't hurt! They might have just just forgotten to add 'em.
Sorry, I forgot to post this response from the developers:
March 18, 2016
Hi, I bought your game Odallus: The Dark Call on GOG and love playing it. It is a true to heart Castlevania type game. The community is still waiting for the DLC to be added. We are wondering when it will be added. Please don't let your fans down.
April 3, 2016
Hey BrokenBull, thanks for your email! Actually, we did sent GOG all the files for the DLC. I will check with them why it isn't yet available.
Well...we are all still waiting... (ᴗ˳ᴗ)｡｡｡zzz