Solution
The NI USB-6501 OEM User Guide, linked below, contains dimensions and locations of the three mounting holes on the USB-6501 OEM. The two holes near the USB connector are electrically isolated from the device. The third hole has a metallic pad surrounding it that is connected the board ground via a resistor. Also linked is the page containing both 2D and 3D dimensional drawings for the USB-6501 OEM.