I was able to figure this out finally!
I believe the problem that was happening is related to my older Vizio TV not able to play Dolby Digital Plus (DD+) and could only play Dolby Digital (DD). The Gen 4 Tablo must be passing DD+ to the Roku. I read that the newer Roku Ultra models (4800) can transcode DD+ to DD, but the older Roku Ultra models could not. So on the channels that Tablo was passing DD+ to Roku my older Vizio TV was not able to deal with it and that resulted in a blank screen.
I had recently purchased a newer Roku Ultra (4802X) which I had on another TV. The Vizio TV had an older Roku Ultra (4670). I just swapped them so I could get the new Roku on the older Vizio TV. Now the Vizio TV displays the Video on all channels because the Roku was transcoding the DD+ to DD. The Roku Ultra 4670 works fine on the newer Samsung TV because it can use DD+.
Problem solved!