if figured the same thing when kakashi used his kamui on the kunai and the slice on the mask appeared, good that you posted this theory (although it`s not a theory, but more the truth).
For the ones who are wondering how tobis warp-jutsu works, basically it`s the same as kamui, only that the warp is not created on a distant object, but directly on the source of the power which is the sharingan (that much really everyone could figure out)....so as long as it sucks your whole body in, the warp will not harm you but instead send you to another dimension like any object that is warped, from which you can escape back by warping yourself again. with enough aquired experience, kakashi would be able to use his kamui to travel through dimensions like tobi does, but as you can see he is just beginning to understand the full potential of that eye technique.
