I may be wrong, but I don't think many diesel-electric locomotives use any form of regenerative braking or battery power storage. I've read that many of them do use dynamic braking but the electricity produced is ran through resistors to produce heat. I'm sure someone is working to capture that energy but you'd really need some very powerful batteries (or ultracapacitors) to handle so much current.

If that's the case, then they really aren't hybrids, IMO. A hybrid gets part of the drive energy from stored electrical power. For a diesel electric locomotive, the diesel engine turns a generator that powers electric motors to drive the wheels. This has proven a more efficient arrangement than using a transmission like on a diesel truck. Back in the 1940s, there were a few pure diesel locomotive made but their narrow torque band meant the transmission had to shift gears frequently. They were quickly pushed aside for diesel-electric engines that were more efficient and needed less maintenance.

For those interested in different arrangements for hybrid vehicle designs, there's a pretty good article here. I've often wondered why serial-hybrid cars aren't available. Perhaps there are cost constraints or other issues such as driveability. I really don't know.