Don Cheadle's character is Buck Swope, a stereo salesman and part time actor whose ultimate ambition is to own his own chain of stores that supply electronic sound equipment, especially stereos. We see Buck constantly hanging out with Jack Horner (Burt Reynolds) and his crew of friends and film co-workers. He even has a short-lived relationship with porn actress Becky Barnett (Nicole Ari Parker), and eventually marries another porn actress, Jesse St. Vincent (Melora Walters).
However, while Buck is seen at parties with this circle of cohorts, he is notably absent in scenes that take place on a movie set. He could be an actor in such pornographic films (and his first name appears to invite a plethora of prurient stage names), but we never see him act in one, especially not in a sex scene.
Ultimately, it is strongly suggested that Buck participated in such films in the scene where he applies for a bank loan to open a stereo store. He is denied for the loan because the bank employee (Don Amendolia) notes a reference on his bank form, and flatly states that Buck is "a pornographer". Buck defends himself by replying, "I'm not a pornographer, I'm an actor."
This reply could mean that Buck does not consider pornography a disreputable business, and resents being negatively labeled a "pornographer" regardless of whether or not he participated in such films on camera or off. Conversely, it could also imply that Buck played a role, or several roles, in such films that did not require him to have sex on camera (i.e. a walk-on role, an extra).
So to say that Don Cheadle's character is a porn star is misleading. "Boogie Nights" never shows Buck participating in the filmmaking process in any role, but no character ever said he did or didn't either. Regardless, the bank scene alone serves as a powerful reminder of the porn industry's contemptible reputation, and the stigma it places on many of those who even have minimal involvement within it.