Shadow map creation is not a post process shader, so that question doesn't make sense.
Then thats why I'm having difficulty, because my shadowmap is created as a post process shader. My shadowmap RTT is declared inside my post process shader and that shader then processes each vertex in the scene. But it sounds like this is wrong and I need to declare the RTT in my program and pass it to every object shader to get updated, then pass the final shadowmap texture to the post process shader. Is that the way it's meant to work?