San Juan and Shavano - Yes

I'll start this by saying a lot of what I am saying here is for aurguments sake.
Well if you are talking about the San Juan and Shavano trains then, yes, there were no combines on those trains.
But if you open up the question to an earlier time to the local trains, that still ran combines, then the answer would be that those particular Passenger equipment was never equipped or rebuilt to handle Electric Lights.
Most of the Combines were sold off to Mexico in 1942 and were never upgraded to have Electric Lights.
But for the sake of a discussion, I wouldn't want a Delco Light Plant in the car with me. Even if the Combine had a partition, it would be too noisy. Baggage cars just seem to be a better fit
Kevin Cook