D..
I would like to ask what kind of symptoms he is showing for you to be concerned specifically about vocal cord issues. Does he have hypernasal or hyponasal speech? Ask about deep nasal pharnx and submucous cleft palate. DO NOT accept that just because he doesn't have a bifid uvula, that he can't have a submucous cleft.
Also find out if he has a short soft palate. That's important to know. I highly recommend getting a nasal endoscopy done. That makes it so you all can see his structure - otherwise, it's just guesswork, and you need to know difinitively if there are structural issues causing this.
Dawn