The Nitrox team have made an incredi mulyer mod for Subnautica and it fully works in VR! You can play VR with VR or VR with Flatscreen.
Nitrox for Subnautica ยท Subnautica Multiplayer Mod
Visit their website. There's plenty of guides there to get going along with a Discord to get help.
To get it working with VR, the next version will have VR launch options. For now, here's a temporary work around.
You'll need to download and run one of these patchers to force your game to launch in either the OculusSDK or SteamVR SDK
Just copy the exe you want to the root folder of Subnautica, then run the patcher for the version you want to use, then you can start your game with Nitrox! (make sure the install folder you choose when installing is the base game folder. If you installed it to C, it should be C:\\Program Files (x86)\\Steam\\steamapps\\common\\Subnautica
)
I'm looking into fixing this, but you currently cannot start a game unless you turn on the "gaze cursor" in the Subnautica settings that emulates a mouse with where you look and pressing the "start game" that way.
Note: A couple things to keep in mind.