I don't have first-person experience with this, but I have heard about people being interviewed for articles in New Yorker, and they have been contacted by exactly those people - whose job was to verify the facts in the article (different from article writer, editor, etc.). I am not sure how widespread this practice is, but these people certainly do exist.
I have met lots of journalists. I have been interviewed for stories (on Bitcoin and blockchain stuff) many times. I have never met, heard of or encountered anyone whose job was to independently check facts or talking points provided by sources.