I use my cruise control everyday on my way to and from work and I have never had it cancel or turn off when I used a turn signal. I also have a 2008 Camry Hybrid with ~19K miles on it.
The only time I see cruise control cancel is when you tap the brakes or pull the lever on the right side of the steering wheel towards you. Even then the CC stays on but is not actively controlling the speed. Moving the lever up and releasing allows you to go back to the preset speed (RA +).
You can either turn it off manually or it will go off when you shut off the car. That is the only two ways that I am aware of to turn it off. Turn signals should have no effect.
What page of the owner's manual did your dealer say describes that "feature"?
