Indeedly. I did a test and I managed to get it working with 5 players. It can be a bit finnicky to set up though, and I've encountered weird random problems.
I'll have a video uploaded later showing this in action.
I found it strange to begin with and it did seem like a bug, but I don't notice it anymore. To be honest, if I could choose between voice and no voice, I think I would have chosen no voice anyway. It just gets repetitive in the long run and it would be annoying to have the person talk whenever you get a secret boss.
I haven't looked into this, but I got a feeling it might be hard coded how certain actions are tied together.
If you consider unique weapon loadouts there are 16. So that's a pretty high number compared to RE4's 4 or RE5's 8.
It's the same outfit. It just didn't render correctly when used in another stage, and what happened to not render correctly was her entire outfit.