per pixel buttons are specificly for the perpixel frames, and your frames will have no buttons if they arent done.
are you asking if yr uis buttons can be png? if so.....yes of course.
but if your talking about pp buttons in general in relation to the pp frames.......they have to be done together, and besides, most frames are pp, not uis, so to not have them is a bit short changing, if you know what i mean.