It’s a mean joke, but it’s fair game. She’s a public figure, a comedian, and she’s using that to express a political view.
The joke may be dark, but it isn’t that dark. It may be mean, but it’s way less than the sheer hate-filled venom she usually gets.
Trying to act like the holocaust is out of bounds for jokes that aren’t just veiled hate is bullshit. The dude is fucking Jewish, they get to make holocaust jokes if they want. In truth anyone can, but you gotta tread lightly.
Does it make the guy a prick? Yeah. He’s not working as a comedian, so he’s definitely an idiot for trying to do jokes on a public forum. But the joke itself isn’t the problem.