Hello,
No, this is not required. The thermal data provided by Wolfspeed (Cree) is temperature-dependent, so the losses will vary depending on temperature. The on-resistance parameter is simply to provide a fixed Ron to the electrical simulation, which runs in parallel to the thermal loss calculation. The impedance of the device could be important if you have parallel devices (such as including an external Schottky diode) and want to ensure proper current sharing between the two devices for accurate loss calculations of both.
Kris
