Yep! When you @ tag a Lemmy community account it posts to that community as a post regardless of what type of fedi account you use. The formatting is a bit weird though, it grabs the first few sentences of posts and puts them as the subject
It can lead to some accidental posts though, always interesting to see these pop up (ex: someone trying to message the Firefox mastodon account accidentally posting to the Firefox Lemmy community). We don’t see any other fedi post types except Lemmy posts, so we don’t really see other parts of the fediverse unless they @ tag the communities.