Okay play tenkaichi 1, now when a person does the rush moves, a split second before they hit you with it, they are vulnerable to 1 a power hit or 2 a teleport, you will see it because they will fail to start the attack.
Now in tenkaichi 2, it isn't there, well i didn't think it was there, but it is, think of it this way, it is like dodging a beam, right before the rush gets to you, Hit the X button to do a step in, yes it is a close combat move so they have to be up in your face, this is easier then teleporting i tried both, and the stepin moves save me way more.
Against omega shenron at the end of the game, he went to do a dragon thunder to ssj4 gogeta, i did the step in move, hit him stunned him and hit him for 20k of my own dmg, instead of taking 33k of his, see what i mean now?
Also yes you can do a step in stun, like i said they are vulnerable to anything, you could do a stepin flying kick if that floated your fancy, personally i like to step in then intate a combo, but that is just me.