My DS was in two 30 day programs that both had a no smoking policy. In their admissions paperwork they cited recent studies, IIRC, that stated that by stopping all addictive behaviors a person had a better chance of success. They didn't allow caffeine either.
That said- I'm not sure how successful the policy was. In both instances, the smoking issue became THE ENTIRE OF FOCUS of every addict there, lol. And, that was pretty much everyone of them.