A Lemmy post will often refer to a specific web link. Is there an API for the linked site to be notified about Lemmy posts referring to it (e.g. to be able to link back, or even to integrate Lemmy comments)?
But I don't think they are supported by Lemmy right now.
Making Lemmy work as a comment engine on a static website was suggested before and should be relatively easy to do with the Lemmy JS client, but so far no one has implemented it.