"record via the webcam in webm format?"if you record it in just about any format you can always convert it to webm but yes you should be able to record in webm
you could try the screen recording software Simplescreenrecorder(very good) "Will any webcam work?" no it has to work with free software you can search on h-node for webcams that work with free software https://h-node.org/webcams/catalogue/en
