Not really. Also Lemmy’s and Mastodon work pretty differently. They may want to like something, but not up vote it. They may not even care about the voting system and not want to participate. Also on a technical level, it’d be messy to make the two compatible.
Well ActivityPub isn’t 1:1 interoperable all the time. Like you’re not going to see the upvotes/downvotes of a Lemmy post when viewing from Mastodon. Which this makes sense, since how would Mastodon even know how to handle that data, and it opens up all sorts of compatibility problems. What does interoperate is the post and comment content which is the important part. Also that you’re able to post/comment to other user posted content even if you can’t see all of that ActivityPub’s application data.