if the usb supports power to the port (which the iconia a500 does) then you could probably use it though the a500 already has cameras on both sides so if it is just to take higher quality picture and video it makes sence
The A500 already has a rear and front facing cameras. 5MP rear & 2MP front. If your USB camera has higher than that I'd be surprised. On my internet computer I have a 3MP and that waas the highest I could get 5 months ago. Most USB cameras are about 2MP. I see no sense in using the USB camera - except in special circumstances.