This is an important question to ask if you are considering radiation treatment. Good that you ask it.
I think generally that CK/GK do not make balance nerves worse or better. If you have only slight balance dysfunction, or none, you should be okay after treatment. If it is more severe, though, this can be a problem. Dr. Hodgson had me go for vestibular tests to get a real assessment of my balance nerve function, which came back saying there was only minimal impact on the inferior branch. Maybe you can get those tests too.
If there is a significant issue after treatment, they can try the gentamycin injection, but I believe it also tends to take out the hearing nerve, if it works. There is also a minor surgical procedure called a labyrinthectomy, which takes out the balance organ (and the hearing as well I believe), but does not go in further after the tumor itself.
Steve