Trying the same thing, VBS -> SteamVR + Unity. Seems to just hang up for a long time for me then Unity puts the player in non-vr WASD mode. But running it as build exe works. Seems to be giving "XR: OpenVR Error! OpenVR failed initialization with error code Unknown error (310): "Unknown error (310)"! "
This is kind of annoying since SteamVR is used widely and development with this workflow is important in enterprise. Still testing the above suggestion as a work around.... Will report back.