Well Chuck, I guess I wasn't complete in my explanation. Just to clarify, I QT fish for long periods when appropriate. Then I acclimate them to my display with a float valve fed from my refugium, removing a qt or two at a time until I have turned over the water in the QT substantially. This is usually a one or two day process.
Once I am happy with the acclimation, I release the new fish into the display after normal lights out. My situation is different though since ALL of my fish tend to actually go to bed at lights out. That way the new fish just finds a sleeping area, and when they all wake up in the morning, groggy etc. they seem to accept the newcomer much better.
Not that I always follow this process to the letter, but in most cases I do. But like you said, with a fish the size of that naso, the QT is a bit small. So is mine so I can relate on that issue.
With your system, there are so many fish, they may forget about fish enough to not even realize there is a new one in the tank. Then your primary issue will be fighting among like species. There is considerable discussion that highly stocked tanks take on a different dynamic and that some of these social issues can be treated differently.