Can I use viktor to upload a image file, visualize it in the controller, and then load it into rhino for more processing in grasshopper?
As you might have already encountered, uploading images into VIKTOR is quite easy. You will also need to make sure you have a generic worker and that you add the image to the config so that the worker (which has Rhino & grasshopper). Then if you take a peek at the rhino/grasshopper tutorial we see that you need to activate the grasshopper script using python and I think you will need to load the image into rhino from there!
Hope this helps!