Recently Heidegger's personal journals were released, there was enough anti-Semitic material in there to cause Germany's head of the Heidegger Society to resign. From what we can see Heidegger was an Antisemite, some have argued that his relationship with fellow philosopher Hannah Arendt, who was Jewish in the 1920s would disprove this. But interestingly enough another German PhD, Joseph Goebbels had a romantic relationship with a Jewish woman as well right before he became involved with the Nazi Party, also Heinrich Himmler noted in his diary of flirting with a Jewish woman during his University days when he already possessed strong antisemitic opinions. Your Grandfather is right, Heidegger was a Nazi sympathizer.