So far ... finding this isn't working for lemmy communities while the same lemmy communities work fine on an ordinary RSS feed app (feedly). Still some kinks to iron out it seems.
Actually, it works well enough. There appears to have been some delay from the test community on lemmy.ml that didn't occur with my rss app (feedly), so probably a hiccup.
Posts come through with kinda ok formatting (which is a challenge given mastodon's constraints).
Compared to mastodon, links to external sources are actually provided (mastodon only renders a link to the original lemmy post).
But, it seems that when a link is provided in a lemmy post, a link to the original lemmy post is not, which is annoying.
Still ... It works ... kinda nice once you combine it with lists and making the lists exclusive (ie posts in the list don't appear in the home timeline).
Currently, Lemmy communities appear as group accounts on mastodon which boost every post or comment posted to/in a community. This is effectively useless except for extremely low traffic communities maybe.
It's not clear to me whether this is a Lemmy or Mastodon issue.