Never mind the health aspects: should burning incense sticks be allowed in the office? No general answer - if all your cow-orkers love the smell, I guess there's no issue. Otherwise, I see no difference from "should I eat my durian for lunch in the office?" or any other smell-related activities. (I prefer that smelly and noisy activities, such as lunch, private calls or smoke breaks, happen outside the workspace; but that's indeed my preference - YMMV)