Einstein yes, but he wasn't actually a member of a socialist party, he just supported it personally and wrote arguments defending it.
Oppenheimer, I think not entirely though he was surely sympathetic at least. His wife, his brother, and his best friend were card-carrying communists, but idk of any evidence that he ever espoused socialism/communism himself, outside of hanging out with communists a lot. He was very much accused of being a communist after the war ended, but pretty much every famous person who wasn't a fascist was targeted by mccarthyist witchhunts and accused of being communist
I'm on episode 4 out of 5 and it's pretty good so far. I don't know anything about Last Podcast's political orientation, but I would say this is not explicitly Marxist content like many on Lemmygrad would prefer, but it does seem to be a good objective narration of history and I'm enjoying it