I’m following the furry community on yiffit.net using my mastodon account, and I saw a post show up on my mastodon feed. So I opened up the thread in another tab, and I’ve been faving/unfaving the mastodon post… and the score on Lemmy goes up/down immediately. So yeah, it looks like faves from mastodon are translated into upvotes on Lemmy.
I’ve also seen likes on my PixelFed notifications come in from Kbin.social users on this post that I sent to Lemmy from there - I’m assuming those were upvotes on their end.

I’m now thinking that some of the upvotes on that thread are actually likes and shares from mastodon. Edit: this might only be the case for new posts.

@bristle If you follow @tech, that’s basically how you subscribe. It will boost all posts and comments made within the community, so you can see them.

I am not a fan of it boosting every comment from every post, but that’s actually required in order for those comments to federate to Mastodon (otherwise, you just wouldn’t see any comments from the Mastodon side).

@bristle @tech It’s really cool that it’s possible :3 but I kinda wish there were a way to mute Lemmy communities from a Mastodon home timeline without muting the entire community (unless there is and I haven’t found it in poking around).

It is very nice being able to be on masto and have a list that just streams in any subscribed posts and comments though ^^

Edit: Also, subscribing to a community by way of Mastodon involves following the community tag. The downside to this is, as I mentioned, it appears in your Home timeline