For pizzas that have short bake times, I usually cook the sausage in a pan until the pink just disappears. The heat of the oven during baking will finish cooking the sausage. I sprinkle the cooked sausage on the pizza as it is being dressed, just like any other topping. So there's no harm in putting some cheese over it. In fact, it will protect the sausage from being overcooked and getting crunchy because of being exposed to direct heat.
I often drain the fat from cooking the sausage just to get the saturated fat levels down, and sometimes replace that form of fat with a monounsaturated fat, such as a light olive oil, which is better for you yet retains the mouthfeel of fat that most people like. I especially do this for deep-dish pizzas because of the much larger amount of sausage used.