At least in 5e, the paladin isn't obligated to object to interrogating prisoners because of a loose definition of "Interrogation" and "Torture". In my experience playing D&D, I've only ran into one hardass GM who insisted that any Lawful Good character, paladin's especially, had to reject any form of forced cohesion. That was really the only thing I was worried about when we were told we had to find someone to question.