yes they are totally taught to separate. You craft that skill by not extending your arms so you don't get called, but you are taught when a db is close to you, depending on your move (are you running a 9 or a 5?); you use your hips, shouldn't or elbow to shoulder to separate. You practice it. and your are taught it. Its a legal and good technique too. You are allowed to should rub separate. You can't "bull" the guy, but in the art of making a football motion back to the ball or LOS, you can use your body to gain separation without overly initiating the contact. Then it won't get called and its basically legal.
Just like a DB can ride a WR out of bounds, or to the boundary, if he looks back and uses his butt....Both positions are entitled to position and how you establish that is the art.