Drivers for native ARM-based targets access real hardware, while under WINSCW, you use Win32 facilities to access or emulate hardware. This means that WINSCW device-level code must be substantially different from that used by native targets.
First, you will need substantial conditional compilation. Device drivers will need full testing under both WINSCW and ARM targets. In general, a WINSCW device driver is best considered as a separate project from a corresponding native target device driver.
Usually, in order to implement this kind of code, you will also need to access Win32 libraries. Specify them using .mmp specifications such as:
start wins win32_library kernel32.lib gdi.lib end