Its been on a while since I used terrain on mobile. I can tell you that it does work. From what I remember there are limits to the number of textures/layers you can use. In ES2 it is pretty limited, I had 2 layers and was limited to 3 texture samplers. Regardless of how many texture samplers the stats say are available. On ES3.1 it should be a lot better but have not played around with it much.