I'm kind of boggling at the idea of these two being a crack pairing when I've read a fair amount of fanfic with them. Songwriter-composer is a pretty natural combination and there's lots of ways you could justify them making a connection.
Actually didn't know that Umi was a songwriter, almost all of what I know about LL comes from dynasty scans dot com. The pair definitely makes sense in that context, though, it just comes off as crack when depersonalized like this.