Most brands of chicken sausages do not contain any nitrates but to be sure look on the packaging for the ingredients because some brands of chicken sausage may contain nitrates although the majority of chicken sausage is nitrate free.
Also most chicken sausage that you buy contains no chemicals or preservatives which makes them healthier than meats with the chemicals or preservatives.
The Chicken Sausage I buy which is Al Fresco chicken sausage does not contain any nitrates so that's ones brand of chicken sausage that I know of that doesn't contain any nitrates.