Heh, kind of funny how I recently added the Karme to my comprehensive list for keeping track of and organizing Federation vessels.
I Wiki-ed moons, and I didn't find any moons with the name Karme, but a Jovian moon with the name Carme, which would be a fitting name for a Luna class. I'm guessing that someone probably made a mistake, or used a lesser utilized spelling, but given that the Karme shows up the most widely under NCC-80117, that is the identification I've accepted for that registry, misspelling or not.
I just go by what the client gave me. Actually I like this spelling bettere than Carme...lol. If he wants to change the spelling I will be more than happy to do that for him.