I've found this pack on Steam page (https://store.steampowered.com/app/1744370/UnMetal__Creator_Pack/).

Description of this pack:
"When you’re escaping from a military facility for a crime you didn’t commit, you’re going to hear a lot of chatter along the way. Guards, infirmary patients, and fellow inmates all just can’t seem to shut their yappers!

But wouldn’t it be cool if that prisoner yelling at you to stop banging on their cell were the voice of your favorite content creator, like Ezekiel_III, Cohh Carnage, Skinnedteen, DeejayKnight, Friskk or Bloodyfaster?

You’re in luck! We’ve partnered with over 80 of your favorite content creators to get their voices into the game. Enter their unique Creator Code in the Options menu, and voila! You’ll hear a confirmation message from your creator of choice to let you know their voice pack is active. Wondering where you can see the names of all participating creators? They're all present in the credits of UnMetal. Enjoy! "

And if YES (Gog version INCLUDE this pack), what Gamers / Streamers / Youtubers donated their voice acting to this Pack?

The pack is listed as a free DLC for the game, just ready to be added to your library.
As for the content creators, the description is the same as on steam, you'll see them (and i guess their activation codes) in the game's credits