No. Cotton balls act as a wic, so could actually draw the water in, if you're not real careful. I lift the chin up to wet and rinse off the top of the head, ensuring that the water doesn't flow into the ears, and by holding the ear flap just so, to prevent water from going inside the ear when washing/rinsing the outside of the ear. I use a wash cloth to clean the inside of the ear leather.
I second Poodleholic! Well said. And if you accidentally get some water in an ear, let the dog shake..I always let my groom dogs shake in the tub, however many times they want...even if that means I am drenched. They can shake that water out. And I always finish a groom with an ear cleaner with a drying agent, to help dry out any moisture that may have gotten in there.
The owner of the shop SWEARS by cotton in the ears, but won't listen when I suggest why I don't use them; consequently, I don't have owners coming back with ear infections, or 'wet ears', and she does...quite frequently, actually...yikes. Sad part about it, is that she makes owners believe that its a normal thing for something like that to happen!!! It makes me sooooooo mad!
And if you don't have any ear cleaner with a drying agent on hand a puff of ear powder will work just as well...