I think it would be a great way to keep cuttings from drying out, giving them a good chance at survival and from the looks of those photo's it worked ... if those photo's are the actual product of the rose cuttings stuck in the potato's. I think I was reading somewhere just recently about someone growing cuttings of some type of plant in potato's but I don't remember where I saw it ... somewhere here on ATP maybe?
I wonder if you might get potato's growing along with the roses? I placed a bunch of potato skins that I hadn't chopped up real well into the compost bin one time and apparently the "eyes" decided to grow and I had potato's growing in the compost.