Webcam simulator for incoming video signals? - Audio/video stream recording forums

First post here, and hopefully in the right section.

Many online conference programs just use a webcam as video source. I need a solution to use a live video signal coming from a switcher to be delivered to the clients. My questions are:

1. Is there a webcam simulator software which can take a video stream from a capture card (like Blackmagic)?

2. Is there a conference software which allows the use of an incoming live video signal?

We want to use Webex but there I don't find that kind of feature.

Thank you in advance for all answers!