Yes, you can wear a ski helmet for snowmobiling. Ski helmets provide excellent protection from the elements and impacts that come with participating in high-speed snowmobile riding. They are designed to be lightweight and comfortable so you won't feel weighed down while you're out on the slopes.
Many of them even have specialized features like heated lining and breathable mesh to keep you comfortable and safe. Make sure your helmet is the right size and fit for you, and that it meets safety standards for both skiing and snowmobiling.