I think the idea is like this:
1V RGB outs from the Vidiot -> Visual Cortex colorizer/compositor channel A. One of the VC composite outputs goes to the Vidiot camera input, providing composite sync for the Vidiot to genlock to. The other composite output from VC (gray RCA cable) goes to my display. This should look exactly the same (assuming default VC settings) as connecting that gray RCA cable directly to the composite color output from the Vidiot.
This sync configuration works for me. Typically I am chaining sync further down, like VC rear sync out -> Vessel RCA connector -> Vidiot -> Cadet I -> Cadet/Castle ramps and VCOs to sync my DIY system to the Vidiot and the Vessel. I have not been successful using the Vidiot as a master sync source, regardless of the position of its loopthru switch – neither my VC or Cadet I will genlock to any of Vidiot’s 3 RCA outputs. Based on this post from Lars I think this is supposed to work, but possibly your Vidiot has the same issue as mine. Since I got a Visual Cortex I just use that as the sync generator and all is groovy.