I have connected my webcam to my Galileo, but I am not smart enough to figure out how to get it to work. I have never played with OpenCV.
I do believe the main purpose for the Host USB connection was to connect a webcam. At least that is the rumors I have heard. I have not seen a web cam in use with a Galileo yet.
If you could point me to some OpenCV information, I could give it a test.