Family just got off Cat 10 days ago and had a great trip (I got to stay home to welcome my third child)... except that the boat with the motor flipped in Big Drop 2 and the motor got a lot sand in it and was unusable... so the last day row out (from TenCent camp after Rapid 26 to dirty devil takeout) was described by the oarsmen as the most miserable and exhausting day they've ever experienced on a river (and there are a lot of river days in this group, most have 2 or more grand canyon trips under their belts and have been running for 20+ years). Lets just say they overestimated the current below the rapids. 12 hours of rowing against a headwind with very little current. Not recommended without a motor, or at least camp as far down as possible and start at the crack of dawn and have two people that can alternate rowing on each boat. Don't count on "good current" to flow you out with ease if there is any headwind, especially since there will be less water pushing down in Sept.
DD takeout was fine.
Next time there is a vow of having at least two working motors in really good shape. My family's group had 2 motors but one was an old two stroke that called it quits 2 miles below Potash, and the other required a complete teardown and clean out when it got home after the flip to get it back in shape. If your group has the resources to have 2 good outboards, its definitely recommended.