I do not believe that there is an obtainable ultimate frame of reference. If one could have a perfectly stationary view that would be very close, but how to tell if it is actually stationary is the issue. This also aplies to hypothetical views from outside the universe.

However, if there is no other matter in the hypothetical universe in which this bucket exists to reference the movement of the bucket against, how can it be observed? Just a thought. Anyways, I think that the water would move to the outsides of the bucket whether there was anything else to reference the movement against or not.