There's likely one spot available if they keep 6. Brown, Beasley, Foster , Roberts and Zay appear to be locks. One spot for the others to fight for and Duke would be in that mix.
Although not likely, these are the other two scenarios for another open WR spot to be available:
If they think Beasley can handle punt returns and find a combo for kick off returns - it could put Roberts at risk. That could open up two possible spots if they keep 6 or they could keep 5 and an extra RB to handle some passing responsibilities (Yeldon).
If they keep 4 RB's and 3 TE's or 3 RB's and 4 TE's. I would think they'll keep 4 of each - so not likely they do this for a 7th WR.