I have not seen stainless steel exhaust systems used on many cars as stock systems. Mostly I see mild steel systems. Any brand or model you're thinking of?
Cobalt can be found in limited places in a car today, particularly in modern entertainment systems. It is found in the magnets for the speakers.
Otherwise, yes...you are correct. There is no cobalt in an automobile nor it's engine.
My Hyundai and the GF's Escape have stainless steel exhaust.