After connecting the new additions to GOG from my Steam account I noticed the DLC for Gat Out of Hell was not linked or not included in the connect.

Does anyone know if the DLC is not included or whether this is an error in GOG Connect?

I have the same situation

Looks like not to include.
Technically, everything is true and logical
This is a separate article
There is not written nowhere that Devil's Workshop Pack is available in GOG conect

so, this can't be error

The API that Connect uses doesn't show owned DLC. Because of this, GOG doesn't have an automated method for DLC redemption.

Hmm, I wonder if there will be an opportunity to manually prove ownership and redeem the DLC?

This goes with how SR4 works. I only have a couple of the DLC's owned on steam yet when I did the gog connect it gave me the century of the year edition which was a nice bonus. I guess paying 2.19 CAD for it is not so bad.