Although you are right that the bubbles themselves do not bring O2 in your water (or your bucket should be 30 feet high) it is not agitation as well.
Let me correct myself: it is and it is not.
What brings O2 in the water is the air pressure of the column of air above your bucket. Even if the water would be totally flat and not moving, there would still get some O2 in your water. But just in the upper layer. The layers of water beneath the upper layer would not get O2 or in a very slow pace.
Agitation of the surface is a way to exchange the O2 rich upper layer with a new layer of water without O2. Then this new layer can get O2 because of the said air pressure and this will happen over and over again.
As long as you have a system that like a conveyer belt replaces the O2 rich layer with O2 poor layers of water, you are fine.
Bubbles do this, waterfalls, flooming, etc.
It is more a semantical discussion