OK, Book of Mormon popped to my head first, but that's not the best example. Neither is the Book of Ruth, though, really.
I would suggest that the best analogies are:
Analogy #1 (which you made): These Dragons are like some of the Catholic Saints which the Protestants (who are based more purely on the New Testament whereas the Catholics added more later stuff) do not recognise.
Analogy #2 (best analogy): The info on the messengers is like the Hebrew Talmud (although unlike the Talmud it is not a collection of laws), in that it was collected later tradition that is not part of the original scripture but nevertheless referenced by many and considered a highly respected source by those who reference it. In fact, divisions in modern Judaism are often based on how much to strictly follow particular interpretations in the Talmud, much like our Messenger division thing.
Since one of the first posts ever said that dragons were creatures relegated to fairytales, it doesn't make sense if they are believed by all of the dominant religion. So probably, the "pure" DL sects recognise the information of the Messengers as an ancient scripture, some consider it to be mostly fairytales and legend which likely contain a grain of truth, whereas others consider it to be true and accurate dogma that must be followed. Those latter people would actually worship the Messengers.