Experts and BHG readers answer.
You are right to ask about the proper perennials for your conditions, but you have several problems to address before you plant a flourishing rock garden.
1. Four inches of soil is too shallow for perennials to thrive. You need more soil, making berms or mini-beds where you can.
2. If you need to bring in more rocks to make boundaries so that you can heap up more soil for small planting spots, make sure you bury them part of the way to keep them secure.
3. Rock garden plants need perfect drainage. Mix in perlite with the planting soil.
4. Your dry shade conditions limit the number of flowering perennials you can use. So be sure to mix in some annuals, like impatiens and coleus, but water them regularly and monitor them for droop so they dont dry out.
That said, here is a short list of perennials for your Zone 8 rock garden:
Ceratostigma plumbaginoides (Dwarf plumbago)
Geranium sanguineum (Cranesbill)
Myosotis scorpioides (Forget-me-not)
Dicentra eximia (Fringed Bleeding heart)
Heuchera x brizoides (Hybrid coral bells)
Asarum spp. (Wild ginger)