Yes and no. What people say is real but sometimes the order they say it in is manipulated or the situations they were originally in that produced what they said.
Sometimes the players or real people are given dialog or talking points. Many times people are simply put in a situation that causes them to act or react. When a person reacts the show's writers /producers make sure the reaction will be dramatic.
A lot of the drama in Reality programming is created in the edit bay. During post production the editors will log a series of 'reaction shots' and then splice them into the episode where they are needed to create or complete a thought or story-line.