Sumac is so invasive if you can keep it from creeping into your neighbors yard it might work.

That weed-like purple campanula is a real bane in my life.

I find that sedum like my west facing steep hill, it is dry. I also have creeping phlox, coral bells and pinks on it. I keep everything short so it doesn't fall over. I live on a hill with one very steep hill on the north side of my house and and a somewhat less steep to the west. You should come to the plant exchange that I am hosting and check out my hills.

I've heard good things, but never used the cultivar Gro-low. I have a Tiger Eyes sumac and although it suckers a bit, it's very manageable. It sounds to me like this is a perfect spot for sumac.