Answer: There are a number of plants that would look good, however their roots do need to be planted in soil or at a minimum gravel mixed with compost or soil. Without healthy roots your plants will not thrive. So you may need to do a little rearranging and/or filling to accommodate their needs. It may be easier to start with small plants and let them grow over time to reach their mature size, thus fitting themselves into the landscape in a natural looking way.
With the sun and rocks reflecting it, your plants will need to tolerate not only sun but also heat. With minimal soil, they will also have to tolerate dry soil. You might consider succulents such as Sempervivum, Sedums of all kinds (some are low growing and wonderful among rocks or gravel), and low growing juniper shrubs (Juniperus procumbens nana is a classic in the Japanese style garden and can look phenomenal with age.) In an overall sense, you will need to limit to just a few types of plant so as to maintain that serene feel of rocks and nature.
Your local professionally trained and certified nurseryman might have additional suggestions based on a more detailed understanding of the planting site and your overall design goals. Have fun with your project!
Q&A Library Searching Tips