My son and his wife did it and said that it was great as you actually get to see the real Jamacia and Jamacian culture.
No, they do not smoke MJ on this tour. The use of MJ or any other drugs are illegal and you could be arrested. The locals pretty much ignore the Rastafairians but you aren't one.

They will however arrest you and it will be very costly for you to say the least.
Jim