Even though this about Red it could be about any plugins because even though I installed Red with Vegas support there is still no Red option in the FX window.
If you already have it installed and have it as a plugin for V4 or 5, just copy and paste the boris.dll files from the video plug-ins folder to Vegas 6 plug-in folder.
I did reinstall already but still nothing . Somebody pointed out that I needed to drop the DLL on the timeline to register and indeed it it ask me to do so when I do it but when relaunching vegas there is still no Boris option in the transition window