just found this encouraging photo too: http://www.vwt4forum.co.uk/picture.php?albumid=12699&pictureid=79342
so a chance it could work on the tailgate version…
edit: just got this very quick response from Roofbox.co.uk:
The bike carrier we tend to recommend for customers who drive vans is the Atera Strada DL 3. This is due to the fact that this carrier also slides away from the vehicle as well as tilting so offers by far the best access to the tailgate of any of the tow ball mounted bike carriers on the market. Unfortunately, I can’t say for definite whether this would enable you to open the tailgate on a Vauxhall Vivaro or Renault Trafic, but it does on a VW T5 which has a very vertical tailgate. If you wish do some measuring, the upright on the Strada DL 3 will slide approximately 45cm away from the back of the tow ball so using this measurement you should be able to gauge whether you will have the clearance required. You may also be able to find this information on an online forum or the like.