Well, now I am confused. As far as I know (having flown with VS for the last 6 years) all full-fare UC passengers receive this service.
Only going on what i've seen when i've been to book with them, only the most expensive tickets in UC get the limo service. If you but the cheaper (but still full fare) UC tickets ie non-flexible then the service is not offered.
A moot point I guess but still they don't offer it to everyone.