For your webcam to work properly with Genymotion Desktop, it must support the UVC standard (USB video device class).
Here is a list of webcams supporting the standard: http://www.ideasonboard.org/uvc/
This is the reference list regardless of your environment (Windows, macOS, Linux).
Genymotion Desktop does not work very well with virtual cameras. However, if you are using OBS Studio, it is possible to use OBS Virtual Camera under certain circumstances. For detailed instructions, please refer to this article.