Yes, galvanisied metal does burn with a noxious green gas that is accumulative, meaning that once you breathe it, it will remain in your lungs. But to get to that point, you have to use a torch, or try to weld it.
However, with that said, we're talking a smoker here, it should never get that hot in the smoker, you want a slow smokey fire, use greener wood, build baffles so that the smoke rolls around your meat. Granddad's salmon smoker was about 8' x 8' with an angled roof, build fire in back, smoke would fill it and continually roll around the fish. Yummy.