At least in SWD, you have to avoid violating the tenents of the faith to avoid penalties or lack of access to AB:Miracles powers. ShadowPriest seems no different (e.g., it's based on Spirit, it allows for "marking").
What are the "tenents" of the faith? I'd put healing/helping somewhere since it comes up in a couple of places. Something about personal gain, since I haven't seen anything about ShadowPriests using their powers to become rich.