Not experienced on boulders, but I imagine that the south facing aspect would help ripen fruit growing up it. I'm thinking figs, apricots, anything that might otherwise just struggle a wee bit to ripen with you.
I have a south facing slope on the side of our drive which I have terraced with our plentiful rocks and hope that the well drained soil will enable more tender herbs to overwinter better for me despite being rather exposed (photo taken in evening).