While I like the thought of a pass rushing DE in round 1, I wouldn't be sure that's what the Cowboys do.
I mean virtually no one thought they would take a center in the 1st round two years ago and a guard last year.
The Cowboys seem to have learned to play the "Let's get a high rated guy (on our board) instead of a 'need' kinda pick".
I would think they'll pick up a FA DE or two along the way so a 1st round DE isn't a must.
Bottom line, I wouldn't get locked in to a DE being the first pick. If the a good value safety, linebacker, CB, DT or even a QB drops, they could very well take them.