As a Chitrali I would have to say that the Kalash are an interesting group, but their is much more to them than the supposed "Greek Connection."
The Kalash religion is essentially a mixture of of the religious practices of the surrounding regions. Ancient Iranic beliefs from the Oxus valley (not neccesarily Zoroastrian, but proto Iranic fire worship), Vedic practices and local animism and Shamanism are all cobined in the Kalash faith.
Their are also thousands of Muslim Kalash. In Southern Chitral (anything south of Chitral Town) the lower classes are all of Kalash descent. A minority of them still speak the Kalash language. The people of Upper Chitral used to refer to all the people of Lower Chitral as Kalash. Essentially most Sunni Muslims (with the exception of certain tribes of Turko-Persian descent) in Chitral, although they speak Khowar, are of Kalash or Pashtun descent. The Ismailies are mostly pure Khow, with Pamiri Tajik admixture.