Resolved Using Unity Recorder to record video from tagged camera in VR

I spent quite a while searching, trying things out, and had a long thread half written out before I solved this so i hope this will help someone at some point.

Problem: when using a tagged camera for the Unity recorder, the video is just a black screen (with the proper audio), and maybe some non-black pixels in a pattern.

Solution: make sure the camera used for recording has "Target Eye" set to "None". Also the camera component "priority" property should be lower than the priority of the main camera on your rig.