does the AC traction motor develop back emf the way the DC traction motor does?
Depends on whether you’re talking about an induction motor or synchronous motor and the motor speed versus synchronous speed in the case of the induction motor.
In the case of the induction motor, the relative slipping between the rotating field set up by the stator windings and the rotor cause (induces) current to flow in the rotor (this is why they are called induction motors). These currents wil generate a voltage in the stator windings in a manner similar to the back-emf on a DC machine.
The synchronous motor will almost always be generating an emf when rotating. The current flow will depend on the relation between the internal voltage and terminal voltage, as well as the rotor angle with respect to the zero torque angle (the greater the angle, the greater the torque). Note that a synchronous motor will be more than happy to act as a synchronous generator if supplied with torque rather than providing torque.
Hope this clears things up more than muddying the waters…
Only in dynamic brake