Might just be my opinion, but playing Nightmare Mode without New Game+ bonuses and trying not to corrupt Aura is pretty much going to be an RNG-fest start to finish. YSQ isn't really all that bad if you've lit the room, get an ambush round, and Charlotte doesn't die R2, but even in Normal encounters like the Ogre Commander can rely fairly heavily on the 50% dodge from Tactical Advantage (especially if you're attempting a fast run w/o using the collar).
As for the the loading screen button, I think it doesn't work in-battle for the same reason that the menu doesn't work. It definitely would be nice since bad encounters are almost always the reason you'd reload a save, though.