I think that the LifeCam Studio needs a specific driver.

If a webcam requires a specific driver then you cannot use two of them on the same system. This is because the driver is designed to support only one attached client device. That's the anticipated use case.

In the case of Logitech webcams it has been possible to tell windows to treat them as generic "UVC" devices. The generic UVC driver is the Windows built-in driver for USB Video Class devices. As the built-in driver it supports multiple instances of itself in use at the same time, each used by a different device.

I've had as many as four Logitech webcams attached to the same system.

Note that the Microsoft LifeCam Studio will usually only deliver 720p30. The camera has a proprietary compression implementation in silicon. When used with the Microsoft driver it's supposed to be capable of delivering 1080p30.

The MS driver gets a compressed stream from the camera, decompressing it to YUY2 in memory on the PC. In theory that means that the client app (vMix, Wirecast, Skype) doesn't need to know anything specific about the USB 2 link or the compression required to deliver 1080p30 over that link.

Rarely does this actually work. I've only seen it work with Skype myself. The MS driver has a huge memory footprint and uses a lot of CPU since it's transcoding the stream.

Probably more than you wanted to know.