It is listed in the update list:
https://www.gog.com/forum/general/the_what_did_just_update_thread/post17076

But the DLC is not in my account.

I have:
Harran Military Rifle DLC
Gun Psycho Bundle DLC
Harran Ranger Bundle DLC
Volatile Hunter Bundle DLC

I was wondering this as well. I thought the Crash Test Skin Pack DLC was a Steam exclusive yet it seems like it might be on GOG somehow?

Thanks. I'm gonna take a look next time i play and make sure i have it. I guess i forgot because i haven't played the game in a while? Also the GOG store page doesn't mention anything about it i believe while Steam advertises it.