as far as I know JP criticizes cultural Marxism and post-modernism, not Marxism at its core.
I’ve watched his lectures on ‘cultural Marxism’ and post-modernism and it’s entirely clear he has very little understanding of either. First, ‘cultural marxism’ is basically a conspiracy theory (originally it was Cultural Bolshevism in Nazi propaganda) which has nothing to do with Marx. Presumably, he’s talking about the Frankfurt School but he never directly addresses the work of Horkheimer, Adorno or Marcuse; probably because he’s never actually read them.
His take on post-modernism he even worse. His summary is that post-modernism says there is no truth so anything goes and is equally valid. He also says it’s the source and justification of identity politics. Neither of these things is remotely true and, like with the Frankfurt School, he does not directly deal with the work of Foucault, Derrida, Deleuze, et al.
His views on gender are ‘redpill’ adjacent at a minimum. I watched one JRE podcast where he basically endorsed alpha fux/beta bux and hypergamy. He’s also hyper socially reactionary and seemed to advocate for some form of forced monogamy. That part is not explicitly ‘redpill’ (if you mean the subreddit version) but that is very appealing to many blackpillers, which is even worse.
I could go on about JP but the point is that yes, guys like him are a pipeline to the alt-right sphere because they advocate for reactionary ideas that, while not explicitly alt-right, rub up against them in many areas. This is partially a function of how the YouTube algorithm works. I myself have been recommended videos by white nationalist channels after watching some JRE clips. I actually like the JRE and I don’t think Rogan himself is malicious. But at the same time I recognize that what he’s doing can be dangerous when he allows nonsense to go unchallenged. He’s not as bad as someone like Rubin (and I think Rubin DOES know what he’s doing), but the effect is similar.