Not that I'm aware.
But there are web UIs you can run that allow you to run a lemmy instance more like a forum, and that could of course be federated with other fediverse instances, including other forum instances.
But not existing forum systems. That's something they have to implement, not lemmy.
Behind the scenes Lemmy speaks a protocol called ActivityPub. It can't just talk to any other similar arbitrary service if it doesn't also support the protocol.
Edit: Apparently the forum systems you mention do/will indeed support ActivityPub. There would certainly be potential for interpretability with the threadiverse, then.