I double checked the instructions and I am following them. To perplex things further I can hook up some UDF's for solid viscosity and pressure successfully, so it looks to just be DPM related.
When I compile any UDF with in-built compiler, I do get the following warning:
C:\PROGRA~1\ANSYSI~1\v212\fluent\ntbin\clang\10\Include\10.0.18362.0\shared\basetsd.h(322,12): warning: cast to 'void * __ptr32' from smaller integer type 'unsigned long' [-Wint-to-void-pointer-cast]
return((void * POINTER_32) (unsigned long) (ULONG_PTR) p);
1 warning generated.

The solid viscosity and pressure UDF's still work with this warning, but not the DPM_DRAG macro.