FWIW, I've twice shot clays with gentlemen who've had red-dots on their shotguns. In the first instance, it was one of the best trap shooters I've ever met. He had one mounted to an 1100 and used it when he was having problems lifting his head. He said that using the red-dot gave him immediate feedback and he'd know as soon as his head shifted even the slightest bit. I only watched him shoot some 16-yard trap with it, but he shot it very well.
More recently, I shot sporting clays with a guy who had eye-dominance problems. He was strongly left-eye dominant, but shot right-handed. He mentioned that he had tried shooting with one eye closed, with an occlusive dot, winking, and so on. However, the solution that worked best for him was a red-dot mounted on his Beretta.
At the first station (which featured a pair of crossers which were a little tricky), I tried not to look too sceptical... and then watched him break them all. IIRC, he ended up shooting in the low to mid-70s on a moderate difficulty tournament course. It wasn't a great score, but neither was it bad. Frankly, his swing looked good and I think he'd pick up more targets keeping his form and simply moving the hold points out a little on the quartering birds. In other words, I don't think the red-dot was the primary source of his missed targets.
I don't own a red-dot currently, but if I ever get the chance to play with one, I'd like to try it for a round of clays. I have a feeling I might be surprised. I also seem to remember that HSMITH posted about using one at some point and doing OK.