I wouldn't consider Sweboz under assymetrical warfare. Yes, Germans ambushed the Romans in the Teutoberg but they had been presented with a perfect opportunity to do so and this wasn't really low-grade warfare. It was an all out assault by an army in hiding. The Lusitanians however were famed for bands of skirmishers who would harass Roman columns then retreat and fight off isolated cavalry contingents which were dispatched to deal with them.