Can I use FaceTime with an aftermarket USB webcam?
As long as you have a web cam internal or external, you will be fine.
OS X Mountain Lion - Technical Specifications
Photo Booth Requires a FaceTime or iSight camera (built in or external), USB video class (UVC) camera, or FireWire DV camcorder. Backdrop effects when using a DV camcorder require fixed focus, exposure, and white balance.
FaceTime Video calls require a built-in FaceTime camera, an iSight camera (built in or external), a USB video class (UVC) camera, or a FireWire DV camcorder, and a 128-Kbps upstream and downstream Internet connection. Making HD video calls requires a built-in FaceTime HD camera and a 1-Mbps upstream and downstream Internet connection. Receiving HD video calls requires a supported Intel-based Mac.
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