Yep, that's a young Melanie Griffith on the poster. She was mauled by a lion, and required plastic surgery. Apparently she received around 50 stitches to her face.
The Hollywood Reporter has called Roar "the snuff version of Swiss Family Robinson." It's truly one of the most insane things I have ever seen in my life. Check out some of the other posters for the movie's 2015 theater re-release..