Actually, neither - the wheel is hub-centric, which requires the center of the wheel to fit over the hub with a good deal of precision. The too-small center won't allow the wheel to fit over the hub, and won't allow proper contact with rotor/drum surface. Too-large center will go 'sloppy' and cause vibration due to radial run-out from the wheel center not being at center of rotation.
The wheels could be machined - lot of trouble, though, and costly. Also kind of hard to get just right.