Yeah, that's an interesting question. Does the PTB thing apply to Buffy.
I quess the closest reference we ever had to the PTB in Buffy was with Whistler. Whistler was originally supposed to cross over to Angel, but the actor who played him had prior commitments, so we got Doyle on Angel instead.
Even so Whistler's interest was primarily with Angel. I personally get the impression that whatever the PTB's agenda is, it concerns Angel. I don't get the impression they care less about Buffy. We've never seen any evidence of it.
As far as Skip goes, I don't trust him or anything he says. He's an admitted liar, with a pro-evil outlook.
Not just Skip either. Do you remember the dead guy in the elevator from Wolfram & Hart. He says something similar to Angel, about how Angel's fate isn't really his own, and his battle against evil is silly and unnecessary.
I don't believe him. I don't get the impression Angel believes him. Can you trust the words of bad people? If your answer is yes, you want to stay away from used car lots.