Arendt actually met Heidegger prior to the rise of the Nazi party. That said, Arendt continued corresponding with Heidegger long after he officially joined the Nazi party. It was definitely a weird, problematic relationship.

What's worse imo is Heidegger's treatment of Edmund Husserl. I don't think it would be a stretch to say Heidegger threw Husserl under a bus when the Nazis came to power.