lavender , sedums, wintergreen with some amendment, dead nettle hosta. hens and chicks will grow in very little soil.

Hellebore/Lenten rose is another perennial that blooms early and is impervious to cold. I've half a dozen of them growing in my southern New England sandy loam. Unless I'm mistaken, they're hardy to Z4.

If you want a native groundcover, partidge berry, Mitchella Repens? Is nice. It's evergreen, has red berries and little white flowers. I have some growing on a rock. Lowbush blueberries would probably do okay, too, depending on how deep the shade.

In addition to the partridge berry and wintergreen/Gaultheria procumbens, there are a number of native sedges/Carex species that would do well. We have a native shrub, Diervilla lonicera (which has the common name of northern bush honeysuckle even though it isn't a honeysuckle, just slightly resembles them in flower and foliage) that grows out across the sparse soil on a mostly shaded large boulder as well as in the shaded sandy road verge. I've seen other natives growing on rocky slopes in shade: Hepatica/liverwort and trailing arbutus/Epigaea repens.

Is the rock loose so it has spaces for root runs or is it fairly solid ledge with just shallow soil over it? That will make a difference as to what might be happy there.

IME lavender, sedums and sempervirens/hens and chicks all need a lot of sun to do well, though they are happy with well-drained soil.

For non-native plants, Gardenweed's suggestion of hellebore may well do all right, though it will want mulch, Epimediums will do fine with poor, dry soil and shade, and IME the old-fashioned orange daylilies/Hemerocallis fulva will do OK if mulched.

Because of the slope and poor soil, most plants will want mulch and slow and deep applicaitons of water for the first season to allow the plants to establish roots.