NBA Teams will definitely draft players on potential if they're a guard.
From last year's first round alone, Rajon Rondo, Oleksiy Pecherov, Sergio Roderiguez, and Shawne Williams were all guards that were just as unproven as Cook. Teams, especially teams like the Mavs and the Spurs later in the draft, will definitely draft guards based on potential. Teams are always on the lookout for the next Arenas or Redd, the natural scorers that get have the potential but are overlooked for one reason or another. You can add Thabo Sefolosha to that list too.