After some more coding and debugging, I've got VBI injection working pretty reliably (and I am _very_ pleased about this!)
Here is what the VBI data looks like on the original Cliff Hanger laserdisc. (I captured this from my disc)
Here is what the VBI data looks like on Dexter (using VBI injection). Note that Dexter only is displaying the data that is described in the official laserdisc standard because this is what is needed to inject the frame number into the video stream. Dexter does not try to re-generate the other non-standard schlop stored on the original laserdisc.