This is the recipe I normally follow when cooking on my conventional oven and as you say can't see why it couldn't be cooked on a smoker
http://www.greatbritishchefs.com/recipes/lamb-kleftiko-recipe (maybe minus the wine on the smoker) Weather's put a kibosh on any chance of cooking outdoors where I live tomorrow. But may well give this a go in the next couple of weekends with either some lamb shanks or a leg of lamb.
Suppose if I try around 180/200F for 4-6 hours after getting a bit of wood smoke on it for an hour first (I gather the recommended internal temp for lamb should be about 160F), Then as you say open up the vents and get the temperature as high as possible , to try and brown the lamb (like homeruk's has) along with the potatoes quickly..
I think a nice bit of wood smoke would add to the final flavour also and be a different