Freewheel diode / capacitor with this board?
The motor driver board is bidirectional: it uses a transistor arrangement called a H-bridge to drive the motor.  

  

The N-type MOSFETs being used as switches in that board inherently contain a "body diode" as a side effect of their construction. That diode is shown as part of the schematic symbol of the transistors. Normally the transistors will take care of the inductive current, but the body diodes will provide a path for the inductive spikes if something goes wrong with the circuitry that controls the transistors.   

If you were to add a diode in parallel with the motor that diode would not only be unnecessary, but it would short out the power supply trough the diode when you reverse the motor.