I would be roasting it!
You could, but I think it would be overkill. A pork tenderloin is a pretty thin strip of meat, with a fairly mild flavor - doing both would probably drown out the flavor of the pork. I'd stick to one or the other.
We usually do a dry rub when we don't have time to marinate it. I agree with amysarah, it might be overkill. Especially on a tenderloin.