I have a 2007 vito spot x van with Brabus 18` wheels and tyres. Inside the fuel filler panel there are tyre pressures listed for various tyres but not the ones on the Brabus wheels. Have contacted the dealer who doesn't know either!
Depending more on profile, if they are low profile I would run them slightly more inflated than standard. If not, probably worth going with the pressures nearest matching the tyre/wheel combination.