I've seen Audi wheels on T2 bay windows and T4 LWB vans here in Australia,
no T3s but they are pretty rare here.  I work for a VW dealer and to be
honest, I would actually use T4 wheels just for a little more margin of
safety.  I don't think there is anything wrong with the car rims, I just
prefer not to risk it.  As a matter of fact I have 3 sets of T4 15" steelies
floating around the dealer and they are noticably thicker then Passat
steels, by about 3mm.  I'll try and find the factory wheel weight limit for
Passat and Transporter.
Ian