No official pay difference between policy and generalist HR in CS. Non-scholars will join the usual MX scheme whereas scholars will join a seperate scheme that pays much higher than MX.

Almost all the jobs on policy / specialist side (not only HR) are for scholars that are not on MX. Your SMU FCH will give a few hundred dollars more starting pay, but it will still be the MX scheme. For super high performer sometimes they sponsor for further studies and the person can move into a different scheme after further studies, but very rare case.