With roof racks, it really depends on what you intend to mostly put on it?
If you need to slide stuff on from the back, then the rhino with the rear roller is good.
If you put heavy stuff on from the sides (as I do) then having a higher side on the roof rack is not too good.
So as with most add-ons it's all relevant as to how you want to use it!
(I know! no help at all but food for thought )
The fixings for a T4 do look similar, but the Vivaro has a 22mm hump on the front and the T4 is flat, so you can't fit a large rack with all 8 fixings, there are some with only the rear 6 but you'll have to measure or find out if they are the same obviously?
I've got the bars on mine which only come on the rear 6 fixings, but as I carry some long stuff wanted the front bar, couldn't get one anywhere,
so bought a s/h back one and modified it, it is not only shorter but sits at a slight angle as well, cut and all welded up and painted, cut the covering boot to fit and bolted it on, first time up the motorway the wind noise and the roof vibrating was horrendous, so had to make an aerofoil for it, all quite now, but 6 hours I'll never get back .
Now I know why nearly all the large racks for the Vivaro have an aerofoil?