The game is not available for sale here, and CD keys apparently will not activate on steam from this region. Could I activate a key on the steam website using Hola Unblocker, or would the gam refuse to download after being added to my account like Wolfenstein the New Order? Is there anything else I can do (that doesn't involve a vpn), or am I just going to have to import the PS4 version?
As this game is not prohibited to run in Germany, you can ask someone from a country where it is available to gift or trade it to you. You can then accept the gift and play it normally. This is an intentional loop hole in Steam and works with any Game that does not have the
onlyallowrunincountries flags on it's config, like seen here. This flag prevents you from playing the game while being connected with a German IP.
The advantage of a Gift is that you do not break the Steam Subscriber Agreement, which you do when activating such a game via a Proxy/VPN.
However, be advised that the developer could change his opinion anytime, but I have never actually encountered that and Techland has left the loop hole open for us with Dead Island 1+2 too. with DI1 it was even possible to activate imported Game Keys.
Source of knowledge: I own nearly every Game on Steam I have as uncut version, gifted by an american friend, e.g. South Park.