The Diesel drives a Alternator producing electrical power to the traction motors in a regular Diesel Electric Locomotive. When the Engineer operates the throttle.. the Diesel engine engages..produces power that goes to the traction motor on the wheels.
A Hybrid version would be.. the Engineer engages the throttle.. which produces power which goes to the traction motors initially.. but also charges the banks of batteries. When the engineers needs the power he can apply to the engine such as in the GE Evolution Locomotive.. Or in a present switcher.. the batteries is what is charged and the engineer engages the throttle to run the traction motors from that bank of batteries..
Links below: http://ge.ecomagination.com/products/evolution-hybrid-locomotive.html
http://www.tc.gc.ca/programs/environment/ecofreight/casestudies/images/idc2-eng.gif
Under the present-day definition, if it moves with something between the internal-combustion engine and the drive wheels, it is a hybrid.
Don't blame me, I didn't make up the rules.