The camera refresh rate has nothing to do with tracking or the display.
It's simply how fast the camera, on the front, refreshes.
While the camera is useful when you first get started I've had my Vive from launch and last month I reformatted my computer and only today realised the camera was disabled when I tried to show it to my friend.
In short, there's no problem with using USB2. Just lower your camera refresh rate from the steam settings, or turn it off if you find you don't use it.