I strongly suspect that the bubbles would not bother the fish in any way. I would just want to make sure that all of the bubbles are able to pass through whatever type of structure you use and not accumulate underneath it.
The floating dock is considered structure and fish will relate to it and use it for shade as well. I think PVC attached to the underside of the dock is a great idea. Panfish will relate to it and larger fish may use it as an ambush point...so the answer is all of the above.
