From my experience the Hoppe's No.9 won't hurt your bluing as long as you don't soak your weapon in it, you wipe your gun down as soon as you are done with it and then a super light oiling afterwords. It does have ammonia in it, and you can smell it during use. Ammonia can cut just about anything if it's on it long enough.
But take heart, Hoppe's has been around longer than I have and if it would damage a gun they would have been out of business a very long time ago.
It is a good cleaner if you have light to medium fouling or residue, and it's fresh. Old residue needs a more effective cleaner.
Any other opinions and viewpoints are certainly welcome wheather I'm right or wrong.