My Boyfriend Has An Extremely Nasally Voice. Are Nasally Voices

My boyfriend has an extremely nasally voice. Are nasally voices natural? He's hardly been able to breathe out of his left nostril his whole life, if he were to get it fixed, would his nasally voice completely go away? I understand everyone's voices are different, but nasality is a result of something, such as an obstruction or overly deviated septum that pharynx thing in the back of his throat right? If there isn't an obstruction, he shouldn't just have a nasally voice, he just wants to get rid of his nasally voice completely.