Yes, and no.
Deviated septum surgery is a common nasal surgical procedure to improve the nasal passages. Septoplasty is another term for this reconstructive plastic surgery.
One should be breathing through the nose during sleep. A deviated septum may contribute to nasal breathing problems and prevent good airflow. Septoplasty is the surgical option to improve nasal breathing due to a deviated septum. Improved nasal airflow results in improved sleep.
Surgery on the septum, however, may or may not improve the bad breath though. Make sure other sources have already be evaluated. Best of luck..