Perelandra as an opera? That'd be interesting... Tor and Tinidril are very operatic names, at any rate. But the Un-Man? I can't see that as much of an opera name.
Yes! Donald Swann set some of Tolkien's poetry to music--and I have that book, and I've learned most of them. Also, he's the 'Swann' of Flanders and Swann...I highly recommend 'At the Drop of Another Hat' if you're interested! He's a great pianist and composer. I'd heard that he wrote an opera for Peralandra, but I couldn't find out much about it. Maybe the music will become available afterwards...? Hm, but yes, the costuming could be awkward. But they always make plot adjustments--usually far too many--and probably that will take care of it.