Yeah, those type of shots are usually comprised of stock cels. Even cels from the famous transformation sequences are stock cels.
Yes, the cels would need to be matted (not touching the glass), and I believe the glass needs to be UV-resistant to prevent light from fading the artwork. You'd best ask specialist framing stores though as I don't have any personal experience when it comes to framing cels.Do you think they would need some special protection if I were to put them in a frame?
rampagess might be able to offer some advice as well as he recently got a Unicron model cel framed.