Yeah, I think what lemvotes does is: act as an instance to receive posts and comments, but only for the purposes of showing the up/down votes.

Federation is pretty interesting, everything is relative, like:

• if you're on instance A posting to a community on instance B and someone from instance C upvotes, and instance A has defederated instance C, does that upvote count?
• If you're looking at it from an account on instance C yes, if you're on instance A then no.
• imagine you're looking at this from instance D. Before instance C's user upvoted, maybe you'd never heard of instance C so if someone asked you about that user you'd be like: huh? 404.

At least I think that's how it works, idk I'm not an expert.