Nonoy Tan, 
I looked over this thread again and realized I misunderstood your comment.  I do know that there are chieftains among the Igorot tribes, but I think you were referring the word "datu" not the concept.  As far as the word is concerned, I agree that it is not used among them - I just did not know what term to use at the time.  The Kalinga term for chieftain (according to this article) is a 
pangat (
http://www.cca.org.hk/resources/ctc/.../ctc02-02h.htm).