Rubah, where in the game does it say that Yevon was using the fayth to summon Zarkand? Maybe it says it in a cutscene i missed...but i do recall bahamut's fayth referring to it as the dream of the fayth, not the dream of Yevon.

And you said the fayth cant do anything themselves, and gave that example of Valefor coming up to yuna. But remember...the summons themselves are NOT the fayth. The fayth manifest themselves into the summons when aiding the summoner. And they can and DO interact with people. Hello, bahamut's fayth talks to tidus throughout the entire game, and even towards the end talks to both Tidus and Yuna!