In the latest release of Render Manager, you cannot use Every-Nth-Frame with the Pack Tasks option. If Pack Tasks is on, Every-Nth is forced off in the GUI and vice-versa. Packed Tasks are the only way to use Pulze to calculate things across multiple frames, like a VRay Multiframe Irradiance Map, and the ability to combine this with Every-Nth-Frames is very useful. I know that Chaos keeps threatening to remove IR mapping entirely, but for the time being it remains a very useful tool for speeding up production renders.
-Josh