I can see why its a good idea running Preds and Vindis in pairs, as it strenghtens their role in the game, plus if you lose one you have a backup.
on a side note. I know the Vindi is very fluffy for a IF list and that you are very fond of it. But in my experience it only pays off in those rare few games. It just does it so spectaculary that it kinda sticks with you after that.
I would drop it for another Pred
The only thing more dangerous than serving the Imperium, is not serving the Imperium!