Do you know if its domestic lamb? Reason I ask, the other options would be New Zealand or Australian lamb. If it's domestic, the flavor will be pretty mild and I wouldn't season it much more than salt & pepper...maybe some Montreal Steak Seasoning. The foreign lamb is bred a bit more "lambier" and will take some rub, but I'd steer clear of anything sweet.
Personally, I prefer to grill rack of lamb. If you do smoke it, I'd go hot and fast (275-300) and keep an eye on the internal temp. Anything over 140 (unless you really like well done meat) will tend to dry out the meat.