Albert is right on here. To say that NI Vision and NXT are compatible is kind of a stretch. Really, they are both compatible with desktop LabVIEW. That is, you can write a VI that runs on the desktop PC to do image acquisition and analysis using the NI Vision toolkit. You can also write a VI that runs on the desktop PC that can control the NXT through the Direct Command interface. So you can easily write a VI that runs on the desktop PC that combines these two ideas.
What you currently can't do is write a program that uses NI Vision that would run directly on the NXT (something you'd compile and download using the NXT Terminal). The desktop PC has to be in the loop somehow.
Hope this helps clear things up.
Brady Duggan
National Instruments