Carter and Lewis are similar in that the Cowboys might view them as 1st round talents that could be had in the 2nd round because they came out a year early. Lewis came to OU without a position, having played safety and running back in 8 man football in high school. Right away he stood out on the practice field so much that the OU coaches just started plugging him in at a lot of different positions, thinking they just had to find a way to get him on the field as soon as possible. Finally for his sophomore year they stuck him at DE, where he was behind two long time established starters Jeremy Beal and Frank Alexander, but got some rotation time. This last year, as a junior, was his first season as a full time starter focused on just one position. IMHO, if he stayed in school another year and develops his game he probably goes Top 15, but as I stated up thread he didn't like the academics of being a college athlete and just wanted to play football fulltime.
If he's drafted by the Cowboys, it's probably as Spencer's replacement in 2013 and his rookie year will be spent learning the position and being a beast on special teams and maybe participating in some defensive sub package with very specific responsibilities.