Those are the same but DMP Which stands for Digital Matte Painting, is a lot more complicated than a native 2D Matte painting. In the digital matte painting you need a strong sense of 3D, to be able to create Something special. DMP is lot more alive, in case of camera movement, animations, Parallax and a lot more stuffs; but the native 2D Matte painting, is just a 2D image without any Complex node setup.