A direct view port shake inside the built-in default animation time frame isn't possible since there's no way to modify the interface to read/add that.
You will either need to break the animations into 2 parts and add the shake via event or script call in between, or a timed shake after you play the animation via eventing. (Note that animation in VXA by default do not stick to the viewport x y position, so even if you do shake the background, the animation still stay on its original spot, you will need a script to fix that behaviour so animation will move along with the background)
Or, do the full animation out side the default animation builder using a script to read and call in picture frames, from there, in the script, add the shake. But this will require a full detail of how you want the animation to be made and when you want the shake to work for a script maker to make this tailored script for you.
