That wheel is aluminum right? It's not going to rust. That rust you see is the back of the rotor, I think. I wouldn't think scratching the back of the wheel is gong to adversely affect anything. Unless you put a heavy wire on it. Might start some finish peeling. My Dodge 4x4 is really hard on the front brakes, to the point of baking brake dust into the chrome wheel. No amount of pressure washing, scrubbing, or wheel cleaner of any type would touch it. I got frustrated to the point of giving up. I was standing over the wheel while applying some "Fast Orange" cleaner to my hands, some of it dripped onto the wheel. I came back later and that spot on the wheel was clean. Amazing. This bottle of Fast Orange sits outside by the water hose and it tends to separate in the container. It's no longer the consistency of toothpaste, but is more like water. That's the only way it will clean those wheels. A new fresh bottle of the stuff doesn't work nearly as well. Yes, it scratches them a bit, but they look much better than they did.