1. By default, the Billboard class along with HID class is implemented in the CCG3 DP Dongle firmware. Yes, ideally it can support other USB classes such as UVC but the configuration of the USB interface may be difficult with the existing firmware due to Flash limitation, full speed rate, lack of a parallel interface such as the GPIF interface in FX2LP etc.
2. The datasheet states that there are no hardware limitations to using the USB FS block for other device classes but the implementation for a full-featured USB device controller would have to be done from scratch as we have no examples in the SDK.