When it comes to weight training, its always good to stay balanced, i.e. exercise other muscles and don't just focus on a specific group. Muscles work together, so if you're doing quad exercises, it's good to do hamstring and butt exercises as well. Also, hamstring exercises help support the knee, an added benefit.
I agree with raven, best way to train for hills is to do hills and in my case, lots and lots of hills . But, it wouldn't hurt to do some isolated exercises for support.