George,
Thank you for contacting National Instruments. The Vision Run Time Engine should only be needed if you are using any VI's that process the image. The idea of the IMAQ driver is that you can only acquire, view, and save images. You can do a little bit of image processing with the IMAQ driver like converting picture formats but anything that uses image processing VI's will need the Vision Run Time Engine. So if you are only acquiring images, etc..., then you will only need NI-IMAQ 3.X.
Regards,
Mark T
Applications Engineer | National Instruments