I reported about the process behind the new arrangements in this Twitter thread:
https://twitter.com/jkermarrec/statu...66787336769537
As you can see, Hidenori Miyanaga definitely consulted with Nobuo Uematsu, but it seems it was just some global advice about what he couldn't do at the time that they could try and "fix" this time around. Miyanaga and his sound team simply tried to elaborate on Uematsu's thoughts when they wrote down their orders for the arrangers. So I guess "supervising" is a bit too strong of a word, maybe it would be wiser to talk about advice giving.
In any case, I'm very fond of the new soundtracks, and I'm especially enthusiastic about FInal Fantasy III, even more than FFIV. There was no way to do something that would appeal to everyone, and I'm fine with them taking bold decisions.