This is taken from VW's warranty conditions:
Depends if you view the wheel caps as part of the bodywork.
Body protection warranty
All current Volkswagen vehicles are fully protected during manufacture against through corrosion for 12 years from the date of first registration (6 years for the Sharan models).
The only preconditions are:
The defect must be reported to a member of the Volkswagen Authorised Network as soon as it is discovered and within the warranty period.
The perforation must not have been caused originally by damage, neglect, insufficient care or maintenance or by external rusting.
A member of the Volkswagen Authorised Network must be advised about any rusting as soon as it is found.
All body repairs will be carried out promptly in accordance with the manufacturer's specification and procedures, using only approved parts and materials, so the original level of anti-corrosion protection is maintained.