As far as timeline-based tweening goes, graphic vs movieclip doesn't matter. They can both be tweened on the timeline. As far as code-based tweening goes, because a graphic symbol cannot be manually assigned an instance name, you cannot directly target it like you can for a movieclip. You would have to use getChildAt() targeting to be able to manipulate the graphic using code.
One primary difference between a graphic and a movieclip is that the movieclip can exist as an animation on a single frame of a parent timeline. Regardless of how many frames you extend that movieclip along the parent timeline you will only see the first frame of it when scrubbing the timeline. But when you test the file, the movieclip will play thru while it is present.
Graphic symbols can also be animations that get placed in a parent timeline, but they can only animate if they extend along that timeline for the same number of frames that they contain. Unlike movieclips, if you scrub the timeline for such a graphic symbol you will see its animation play out as you scrub. So if you have an animation that you want to place in timeline and you want top be able to see it animating while scrubbing the timeline, you would want to use a graphic symbol and spread it along the timeline for the same number of frames that the graphic contains. If you extend it less frames it will not complete. If you extend it more frames it will play over for as many frames as it has available.