This doesn't seem to be something driver specific, and instead I suspect that this would better be done somewhere in win32u, with the KBDNUMPAD flag.
Fwiw, it'll probably require more work in the stack but IMO the drivers shouldn't have to provide a vkey in the events they send to wineserver, and the NtUserMapVirtualKeyEx call would also probably be better done on the receiving side of win32u.