The short answer is, yes. Most, if not all professional photographers apply some editing to their images, but the amount of editing varies for each photographer and what final image they are trying to create.
No camera is completely perfect, and there will usually always be a couple of very slight tweaks on lighting or color to make on any image. If a photographer's images look especially creative or stylized, then you can bet they have edited the image extensively.
Editing images is also a great way to add your own signature style and personality to an image and get future photos instantly recognized as yours. If every photographer used same the in-camera JPEG, wouldn't that be boring!