It's simple to give a general answer. If you look in any class of the Sprite Kit Framework Reference, or any Apple Framework for that matter, you'll find a paragraph named Availability:
Every description for every method and property of a class has this mentioned. If you were to use above method or property in your code, your app is going to run (without crashing) only on devices running iOS 7.1.
Armed with that knowledge I'm certain you'll find the answer to your question. In general and if in doubt, if it's a new feature of a new iOS version the answer is no, it's not going to be backwards compatible unless stated otherwise in the class reference.