Most of the "contests" (shows, exhibits, etc.) I have entered have pretty strict rules clearly stated. Some have separate categories for "manipulated" (and they describe what they mean by that) photographs and they are judged separately. Some do not.

I know most folks here will probably attack me for this, but I'm a realist when it comes to my photography. That comes from years of being a photojournalist. Even in my "artistic" work, my desire is that someone can actually go to where I took an image and see exactly what I portray in the image. That precludes my changing skies or moving objects. If I were to do that, I would not call the finished piece a "photograph," but perhaps "digital artwork." I do not deny that folks have the right to do any manipulation they see fit, but I do hope they will own up to it. I admit to being disappointed when I see a beautiful capture posted, only to find out that it is a composite. I don't mind that it's a composite. Many of them are beautifully done, and I admire the originator's ability to do that. What I mind is that someone claim to have captured that image as one click.

I've alluded to this many times, but never so clearly and concisely.

Pretty much if a picture has any value other than forensic, you can safely assume it's been "manipulated."
Photography only begins with a picture, it ends when it's good enough to be proudly displayed on your big screen HD TV