I am not sure if cut planes work with an unsteady solution at all (i.e. do they cut as the solution progresses, or only at the end of the solution?). If they do work, I am pretty sure they do not rotate with the solution.
If you are running an isolated rotor, you can place the rotor at Y=0, Z=0 and align the rotating axis with the X-axis. Then, VSPAERO can perform a steady solution where the world rotates and the propeller stays still.
If you start with one blade in a particular orientation (say out the Y axis), then you should be able to get chordwise dCp distributions.
This is only available from the command line, there is an old example here:
Rob