I have no experience with this, but can you view the RTP stream on the Windows computer with something like VLC?
The virtual camera support of Unity may be a little tricky to get working. See this last post. A community member sent me information that using the older Unity plug-in for virtual camera support might work.
Can RICOH THETA Z1 be used in Unity as a webcam? - #30 by craig
You may be able to go to the TwinCam Go research project and figure out how they get the stream to display in the headset.
Telepresence Using THETA V and Segway by TwinCam Go
As they are an academic research project, they may have published details on their implementation, possibly some open source code.