UseWayPointZ is for pulling with advanced path. What this tells the pull routine is to use the Waypoints Z when checking the mobs Zrange based on your MaxZRange. This way you only pull mobs in the Z range of your path.
PullRadiusToUse is so you can control the Percentage of the range of your pull item/spell/range. This allows you to better control just how much area you want to search for mobs to pull. In an open field where mobs are always stationary you can set this to 100, where in zones where mobs are always moving, you can set it to 85. Now when you are running up a narrow path and you only want to pull mobs that are inside a narrow path you can set it to 35 or 45, it is all depending on the situation. It allows for fine tuning how far away from you or the path waypoint you want to search for mobs to validate for pulling.