Certified GKH Gardening Expert
Unfortunately, mixing baby toes and living rocks probably isn't a good idea. Both have low water needs to begin with, and when they go dormant, they shouldn't be watered at all. The dormant period for these two plants are actually at opposite times of the year, so planting them together would result in one always being over- or under-watered.
You can read more about baby toes here: https://www.gardeningknowhow.com/ornamental/cacti-succulents/baby-toes/growing-baby-toes-plant.htm
And more about living rocks here: