Pork sausage patties in a crockpot overnight
It really depends on how warm the warm setting keeps the food. If it's over 60 degrees Celsius, you should be fine, but for something like pork I would want it to be considerably over that temperature to be on the safe side, and then you're into cooking territory rather than 'keeping warm' territory.

You are probably better off cooking the patties, storing them in the fridge, and reheating them, wrapped in foil, hard and fast in the oven, if you're looking for a quick, convenient way to serve them first thing.