Most passenger trains in the heavy weight era did not even include an observation or tail car in the consist. Long distance name trains ( ei: 20th Century Limited, Broadway Limited, Royal Blue, Super Chief, etc. ) of that era usually did have an observation car in the consist. Railroads also would occasionally tack one of their heavy weight business cars ( usually a heavy weight observation car ) onto the rear of a passenger train.
A caboose at the end of a common carrier passenger train ( pre - AMTRAK and certainly during AMTRAK ) would have been rare as hens teeth, however, in the world of railroading I would not be surprised if somewhere it may have happened once or twice for some very odd reason.
As stated by Dominic M., earlier in this thread, the PRR included a caboose on the end of mail and express trains for a period of time. These cabooses were fitted with high speed passenger trucks. I've also read that the B&O also used a caboose periodically on mail and express train out of Jersey City.
