Solution
As of Vision Acquisition Software 2010, you can acquire true U16 bit images in both NI-IMAQ and NI-IMAQdx.
If you are using NI-IMAQ you will need to add the attribute Unsigned16BitImage (Yes) to the camera file underneath the InterfaceInfo for your specific frame grabber. A camera file with this attribute added is attached.
If you are using NI-IMAQdx you will need to use an IMAQdx property node with the attribute
Acquisition Attributes» PixelSignedness: