They are in no way "Schaffner" although get called that way...
They do not have any legal responsibility regarding tickets/passports but as a courtesy to ease travel for customers they collect the tickets (and passports if crossing borders) so passengers don´t get disturbed in the middle of the night because of ticket inspection by the "real Schaffner" or customs officers !

Btw.: I worked a few years as Triebfahrzeugführer (engine driver) for Deutsche Bahn so i know a bit also on these details ...