Yes you absolutely can! Any mustard will do, as will a light amount of oil, I have used hot sauces, like Tabasco, Cholula, Siracha. All come out good, and in general only enhance the flavor. Since we are cooking the pork ribs low and slow over a longish period of time, the flavors even out, so even when adding the hot sauce it isn't crazy spicy.
The best thing to do is experiment. Try different things, and see what works for you and your family or guests.