I made the mistake of going to their /b/ board one time. In short, yes, people do. Horrifying gore, too. Just basically don’t. Like, ever.
The problem with the comparison here, however, is that that place moves incredibly fast and deletes everything automatically and permanently. Even if the feds came knocking for 4Chan, there’d probably be nothing to show. Lemmy, on the other hand, apparently caches everything locally until you manually purge it (so I’ve heard).