Dear Sina,
The total drivetrain (rotor + generator) inertia of the NREL 5-MW baseline wind turbine is documented in the following forum topic: What's the exact meaning of HubIner? - #8 by Jason.Jonkman.
The equivalent blade-pitch-actuator spring and damping constants stated result in a second-order transfer function (with a natural frequency and damping ratio) rather than the first-order form you are showing. Thus, there is no true equivalency. That said, the frequency of the second-order actuator is very high–as if the actuator does not exist. This would be equivalent to a very low value of tau_theta in your first-order transfer function.
Pitch faults are set by the override pitch maneuvers defined within the ServoDyn module.
Best regards,