No, diastasis recti is a stretching (sometimes severe) of the connective tissue that runs down the midline of the abdominal wall.  A hernia is when that connective tissue tears.  A severe and untreated diastasis can put you at risk for developing a hernia and some people have both a diastasis and a hernia.  However, the rehab process is very similar and even hernias that need surgical repair benefit from Functional Core Rehab before and after surgery.