It'll be grossly non-compliant with the USB spec if not, but the thing you have to take into consideration is the wattage. Apple likes to provide basically the weakest charger it can get away with based on how much power a particular Macbook model will draw while in use. I believe it's a 29W for the Air, 61W for the 13" MBP, and 87W for the 15" MBP. So while you can technically use any charger with any machine, if your machine draws more than the charger then it won't be able to keep up while you're working (plus, running the device at a charging deficit like this will wreak havoc on the battery).