They love rock walls Sharon. They are alpine plants, the rocks would give them very good drainage. I took some to my sister in Wenatchee, WA and they love her rock wall. You would have to play around with different varieties to see which ones would do best. I have a tectorum that will take just about any condition.
Linda (LuvNature) lives in TN and grows them. Hers have done very well. They are really tough little plants. Something else that would be great in your wall is sedum and they look so nice inter planted with semps.
Here is one of my raised beds with some sedum growing in the middle. This particular one would be too tall for your rock wall, but some of the low growing ones would be beautiful. The coral colored one (Coral Reef) to the left of the taller Blue Spruce is a low growing sedum.
Sedum senanense would be wonderful in a rock wall. Mixing the sedum and semps around the wall in separate pockets would create a lovely tapestry affect. There are many leaf shapes and colors on the sedum.
Please let me know if I can help you with finding what would work for you. I have many different varieties of both semps and sedum.
