Searching the web, it is not clear if Java 8 is supported for Android development or not.
Before I download/setup Java 8, can someone point me at any "official" documentation that says Java 8 is or is not supported for Android development.
Yes, it's possible to use Java 8 for Android development as Android supports all Java 7 language features and a subset of Java 8 language traits that differ by platform version.
Here's an “official document” which states:
We've decided to add support for Java 8 language features directly into the current javac and dx set of tools and deprecate the Jack toolchain. With this new direction, existing tools and plugins dependent on the Java class file format should continue to work. Moving forward, Java 8 language features will be natively supported by the Android build system. We're aiming to launch this as part of Android Studio in the coming weeks, and we wanted to share this decision early with you.
Check here for the Future of Java 8 Language Feature Support on Android.