If legislation and/or the company terms's and conditions prohibit it and he refuses to extinguish after a polite request. Yes, without a doubt! And I would not do it behind his back. I would tell him to his face that I was reporting him. Just because it's a freighter (Dangerous goods etc etc?) does not mean that rules can be ignored. If the rules allow it then fair enough; if they don't then please comply with the regulations. Its not rocket science.
A few voyage reports from non smokers along the lines of "Packs operated in high flow for duration of flight to mitigate effects of crew smoking - extra 1% fuel burned as a result" might cause a tightening up of some company's smoking policies or knock a hole in profit share schemes.
Nicotine patches are readily available in chemists and through AME's for those that can't cope with their drug addiction for the duration of a flight.
I was tempted to ignore Capt Testicles literary eloquence but the point that he has so conveniently missed is that wrt Aids you, by and large, reap what you sow. However, passive smoking is indiscriminate and kills a large number of non smokers. Hence, all the ongoing court cases.
Have a little consideration, please, smokers and respect the legislation when smoking is banned by confining your carcinogenic and foul smelling habits to either the great outdoors or the smoking rooms that airports conveniently provide for you.
If I go to a public place where smoking is not banned and people are smoking then I have the option to leave. That option is not available in an aircraft (freighter or otherwise) and some consideration from the smokers towards their fellow workers would be most appreciated.
Otherwise I go back onto my diet of Guinness, Boiled Cabbage, Baked Beans and Pickled Onions and let you savour the by-products of my bad habits!