Hi,
That's fine, you will still target your gameObject, you will not target your dummy at, the dummy is only here to "rig" your system. Visually it will look exactly as if there was only one object.
it's true that if you had a video or a demo of what you would like to achieve, it would be easier to provide an alternative, maybe you don't need iTween to begin with.
one more thing, you could use "animate float" action, and then inject that value into your transform position only on one axis.
bye,
Jean