Not too long ago, ACE Team announced Zeno Clash's next DLC update, which will include lots of new content, features, and bug fixes for the game.
However, in addition to the aforementioned features, this will also come with a special "compatibility pack" which will enable the models from the game to be used in Gmod as easily as any other game's content.
For more information, and to check out the official announcement yourself, see the post Zeno Clash developer Carlos Bordeu made on the Steam forums, or check out the Facepunch topic where this pack was further talked about.