THETA driver for windows(v2.0) and Unity may work with the virtual camera output of the OBS.
Although the integrated virtual camera of the latest OBS does not work with Unity, the older plugin version seems to work with Unity.
Unity seems to be aware of this kind of webcam issue,
https://forum.unity.com/threads/webcam-capatibility-not-work-on-publish-setting.857095/#post-6578806
If anyone has time, suggest sending a bug report to them.