My take then: "The 49ers easily could have handed the job to Culliver after the 2011 third-round choice played better than 40 percent of the defensive snaps last season. Adding Cox creates competition and improves depth at a position that has become increasingly important as more offenses use additional wide receivers. ... Culliver seemed to fade some late in the season, no surprise for a rookie making a significant jump without the benefit of a regular offseason. He figures into the 49ers' plans no matter what, but will Cox siphon off some of his playing time?"
The update: Cox is indeed making a push. He played multiple spots in the secondary during the exhibition opener against Minnesota. Cox stood out with an interception and a tackle in run support. Like Culliver, Cox can defend the slot or the perimeter. Tramaine Brock is a factor as well.
Culliver was ahead of Cox on the depth chart against the Vikings. I didn't notice him much, which can be a good thing regarding cornerbacks. Culliver also seems to have had a strong camp. But with Cox making plays on defense and special teams, this is a competitive situation.
Officials did flag Culliver for pass interference. There was contact on the play, and lots of it, but in reviewing it several times, it appeared as though the receiver, Kerry Taylor, had not exited the 5-yard zone where the rules allow for contact. Taylor was right at the five-yard mark when the quarterback released the ball. At that point, rules prohibited Culliver from playing through the back of the receiver in an attempt to defend the pass. Culliver was playing aggressively near the line of scrimmage and got caught when the quarterback threw the ball.