There are standards for kerosene stoves and heaters. They can't produce unsafe levels of carbon monoxide. In fact, the wick design system is safer to use than a gas fed burner. Many people have gas fed burners as a home furnace or a gas kitchen range. The key thing is to make sure everything is working as it was designed by maintaining it properly.
All flames produce carbon monoxide. A candle, a gas range, and even a wood fire or an automobile produce carbon monoxide. Nowadays, people have carbon monoxide detectors to check for a gas leak or carbon monoxide leak. What makes kerosene easier to deal with is that you can see if it spills out or not. With natural gas, it is colorless and in gas form and that makes it difficult to see.