It will be hard to make the cut for the DB if there are few injuries. At corner we have Talib, Peters Robey-Coleman as starters, with a 2nd tier of Hill, Peterson, Shields and Hatfield (plus two other CFAs). I would not be surprised to see 6 but a definite 5 there. At S Joyner and Johnson start, and then there are Christian, Johnson and Countess who were all with the club last year. There are 5 other safeties listed (including Travin Howard a 7th round pick who played a LB in college). So the cut may just be based on mini camp and then number crunch. They may feel 20 DBs is too many to bring to camp. They may want to free up a spot for another position group.
On that note, there isn't much camp body depth at RB. After the top four, Gurley, Brown, Davis and Kelly, there is only the newest ram, Nick Holley. He is the twin brother of one of the camp strong safeties (list as #6 on Ourlands), Nate Holley.