After reading this question, it made me wonder: while the auto sensor cleaning is happening, would the human eye be able to detect any movement?
Point 4 of the accepted answer to this question suggests that the vibration is at a frequency of around 35-50khz. (For some cameras.)
Instinct would make me think that this is just too fast for the human eye to detect, however if the amount of movement is enough, I guess this could feasibly be seen as a blur.
I've never tried to trigger it while the mirror is locked up, but my guess would be that it's not possible to manually trigger sensor cleaning while the mirror is locked up, therefore with normal behaviours of a camera, you wouldn't be able to test the theory.