As far as this discussion is concerned, yes. Exploiting a vulnerability that requires specially-crafted images isn't practical if the images are being generate

As far as this discussion is concerned, yes. Exploiting a vulnerability that requires specially-crafted images isn't practical if the images are being generated by Google. You would need to find a vulnerability in Google's PDF renderer that let you cause it to generate an image that contained an additional exploit mechanism that would take advantage of the GDI bug. Sounds highly improbable.