Thanks very much, Fiji Dive Guy! Do you know if Koro Sun does? And how is their dive operation in general?
I looked at Koro Sun which gets good reviews. However, I had a very good package which was for Cousteau so i dove there.
Here's a thread that might be useful. Look at the Koro Sun facebook page as their website is down.
http://www.scubaboard.com/forums/pacific-islands/231199-fiji-savusavu-dive-operations.html
Send them a message and I'm sure they will respond quickly.
I tend to use nitrox when it's available, but I didn't in Fiji (even though Cousteau offered it). I would would do it on days when you go to Namema or Somo Somo because you'll want some extra bottom time.