"Something can not be proven to be true without showing that it is not false, and something can not be proven to be not true, unless it can be proven to be false."
Since science is not concerned with proving things true or false, this is completely irrelevant. Evolution is a model based on observation, and it works. That's all that matters.
If you can use the model of intelligent design to predict how disease will develop and other such questions in biology, then by all means, do so. So far the track record of intelligent design on the furthering of any and all fronts of biology is rather dismal. And that is what matters.