I am making granola and just realized I do not have vegetable oil. Can either canola oil or safflower oil be substituted without compromising the flavor? 
You can certain lyophilize fruit. It's done commercially and there's no insurmountable barrier to doing it at home. Since water basically 'boils til it freezes' in a vacuum, then slowly sublimes, you're not likely to get much improvement on a dehydrator's  12-24 hour cycle. For some fruits however, product can be much better when freeze dried. Here's some examples of what you can get: Bananas, peas, tomato slices, carrot slices, spinach, beans, mango, whole berrys etc. 