At the moment Lemmy and Kbin federate exactly, Lemmy communities and Kbin magazines federate 1:1 with upvotes, downvotes, comments, all working as expected.
Mastodon users can follow communities and magazines as though they were users, post to them, and see replies. Although they see everything linearly. If you ever see a community post that starts by tagging the community that likely came from mastodon.
Lemmy does not currently, and may never, allow you to follow mastodon users or tags. Kbin offers a microblog view that does display mastodon content in its intended form.