MHP is indeed completely non-smoking -- this is printed on the tickets and is stated on the DLR website on the MHP page. There is a designated smoking area for the parties in the esplanade. I've never seen it, but have heard from other guests who've used it, so ask CMs about the specific location. I have seen guests who light up in DL during MHP be approached by CMs who ask them to put out the cigarette and go to the esplanade to continue smoking.