Woodthrush, not sure how I missed this thread, but here I am finally. : )
Love the plantings in the rocks. Not sure about all the micro climate conditions this is in. If not enough sun the semps will more than likely kind of peter out. If they are getting enough sun they should do very well. You can improve their chances by putting chicken grit or pea gravel around the base of the rosettes to assure good drainage. How long have they been growing in that spot? The moss is lovely, but if the moss is doing very well it may mean in the long haul it might not be the greatest for the semps. However many of the sedum will grow well with the moss. : )