I saw where an alco s2 was a diesel-electric locomotive. With the diesel engine connected to an electrical generator. That being the case with the loco having an electrical generator, would it be possible for the engine to produce hep? (Or is it one of those that can produce hep OR traction but not both.)
No it can't produce HEP (480 volt 3 Phase at 60 Hz)
An ALCO S1 is a DC machine and traction generator does not produce AC power