How about "Hymnatic" (as in fanatic about hymns) or "Hymnatics"?

Or perhaps "Hymnocracy" or "Hymnocrats"?

I tried searching on Google for each of these, and got no hits.

I got only one hit for "Hymniverse" (as in omniverse), and that was at a site in the British Virgin Islands (Slash.McCarthy.vg) because the "word" was used in a paragraph full of encoded lingo in which everything at that site was written. No mistaking that for another forum about sacred music, so "Hymniverse" should be safe for you to use.