Are you referring to basic access of a USB video camera for streaming video with Jabber/Jabber-SDK, or are you talking about remote control of direction, zoom, etc.?
For the former, I think the general expectation is that USB cameras will work with Jabber/SDK, and the active camera can be selected via the Jabber UI or via the Jabber SDK API. If a particular camera is not showing up on the list of selectable cameras, that may indicate some incompatibility with the camera or camera driver.
For remote control, I think you would need to look to the camera manufacturer to see if they have an API/SDK available that could be leveraged by a custom application for control purposes - the Jabber SDK does not expose any remote camera control capabilities.