Symbolism vs. Abstract vs. Visionary?

One of the intriguing aspects of religious artists is how they choose to portray the spiritual. There are some who think this can only be done as abstract art. But abstract art fails in that the viewer frequently has no starting point from which they can interpret the image. For two thousand years artists have built up a rich vocabulary of symbolism in order to portray spiritual subjects.
So-called visionary art is an interesting intersection of the two. It isn't normally the type of art one thinks of as useful to religious artists but there is something intriguing about it. While looking at the art in an upcoming Visionary Art Conference I couldn't shake the feeling that reminded me of the work of St. Hildegard von Bingen

What do you think? Was St. Hildegard the first, maybe the only Catholic visionary artist?