What happens is that the content arrives with 0 votes.
With Mastodon and Kbin I think you're right, but I thought Lemmy deliberately went back and populated it all. I literally just federated https://lemmy.world/c/callofcthulhu@ttrpg.network to test (it wasn't on lemmy.world until I searched it) and it arrived with all the right scores. IDK if that means vote identities go over though.
(Edit: Oh, did you just mean scores were federated correctly but votes were lost? That would make sense yeah.)
That's a very good idea!
Yeah! I think so. It might be worth a post to a wider swathe of the community.