There is source code for this project, but it requires a laptop to run on the code on. Is this not possible in your use?
Successful Theta V stream from drone to VR headset 0.25 miles away
Another approach with a Raspberry Pi as a relay is in this post
Industrial Robot Uses RICOH THETA 360° Live Video To Inspect Tight Places
Can you advise if it is possible to use another device as a relay in your application? Or, do you require the headset to connect directly with the camera?