ZBrush's tablet pressure support is through the Wintab service. However, Microsoft and Sony devices (such as the Surface Pro) have N-trig devices which use a different API.
Microsoft now owns N-trig. For their Surface Pro series of tablets they have a separate drivers and middleware package that includes optional Wintab drivers. This implies that during installation of the package you will have to specifically enable inclusion of the Wintab drivers. You can find this package at: Surface Pro 4 or Other Devices