Unfortunately, due to standard discrepancies, OBS virtual camera software does not work with Genymotion Desktop.
We are aware of this limitation and it is planned to fix this in the future, but we don't have any ETA.
In the meantime, please note that we will implement a new media injection feature with the next stable release, Genymotion Desktop 3.3.0, which will allow to inject video files to the device webcam.