My experience with wet-dry is zero, but that being said I've never needed to expose my bacteria culture to increased levels of oxygen beyond that available to a canister. I don't get dangerous mini-cycles even when I seed from another filter. Cultures of the same bacteria in oceans and lakes have been fine without wet/dry as well. Nitrifying bacteria is tough stuff; pretty essential to all life on earth. Some extra O2 might help, but it's certainly not vital.
For the Wet/Dry part you should have the bioballs, or whatever, out of the water for best effectiveness. Unless you have a high fish load, leaving them submerged will cause no harm. The point of the Wet/Dry filter was to have high stocking levels of critters before people figured out that whole live rock thing in reefs. Wet/Dry was adapted from the water treatment industry where speed/economy of space/cost/time was required.