I’ve found that, currently, this kind of works and kind of doesn’t. I’ve boosted a few lemmy and mbin comments from my Mastodon account, and it shows up in feeds just like you would expect it to. Unfortunately, the parent post of the thread only shows as a link to the lemmy/mbin thread, rather than showing the full text of the original post. So it’s hard for people to see the context of the comment.
Mastodon appears to see lemmyverse comments the same way it sees Mastodon comments, but the top-level post that started the thread is somehow different.
I’ve been loving RFF the last few months, it might be my favorite new thing I’ve found since I switched from Twitter to Mastodon. It also always shows you the artists’ fediverse usernames so you can follow them, and they usually have a Bandcamp link if you want to buy an album.
They recently said that they could use some volunteer help. I haven’t been able to check out what they need yet, but their matrix channel is #radioFreeFedi:matrix.org, I think that’s where they organize things.