The fglrx proprietary driver supports XRandR 1.2, so the Displays capplet will (should) work for it.
The nvidia binary driver does *not* support XRandR 1.2, so (as Daniel notes) the Displays capplet will not work properly (specifically, it won't do any multihead or external display setup) with the nvidia binary driver.
The fglrx proprietary driver supports XRandR 1.2, so the Displays capplet will (should) work for it.
The nvidia binary driver does *not* support XRandR 1.2, so (as Daniel notes) the Displays capplet will not work properly (specifically, it won't do any multihead or external display setup) with the nvidia binary driver.