I still think it's likely to change over time. Especially with updates. But as it stands right now, he's the only composer working on the title.
Yeah, that's why I've been concerned even since hearing their Qs and As. If FFXIV successfully becomes a long-running game like FFXI, they will release some expansions - but will Uematsu still remains a solo composer? If not, why doesn't he hire another composer from the beginning? No more Mizuta, though.
I don't think Uematsu is in particular need of help arrangeing, and Blue Dragon and Lost Odyssey featured plenty of live instrumentation, so I wouldn't worry about that too much.
Uematsu literally always needs helps when he score a game on post-SNES consoles, because he just makes sketchy MIDI sequence data (the recent issue of DTM magazine reveals he only uses piano/electronic piano patches and avoids anything else because he thinks it would narrow down the potential of the sketched track) and it's Kawamori, or Narita who arranges it. Or Nakayama, Hamaguchi and Toyama when orchestrated. I don't think it's an uncommon story as, regardless of whether it's true or not, I've sometimes heard that some of the equally eminent composers like Yoko Kanno or Hollywood film guys are merely responsible for submitting chord progressions but eventually get the credits and acclaims for everything other people do.
The working style of Uematsu holds both strength and weakness, methinks. Without talents like Shiro Hamaguchi or Masashi Hamauzu (who assisted in chorus performance of FF VIII and XI, not to mention his own singing in VII), it can result in just a waste of the budget. For instance, although I know not a few people like it, I think "Releasing Seal" from Blue Dragon could have been a masterpiece instead of being garbage as it is now, with a better performance and lyric (Hamauzu, how about saving "The Unsung War" - the track I also think suffers from the terrible chorus performance?).
In short, I do think Uematsu needs a better help.