Yes, Windows 8 is supported in Unity Integration 2013.1. This includes:
Windows Store App on Intel devices and ARM tablets
However, it shares the same limitations with the native Wwise SDK on that platform, e..g., remote connection (profiler) is currently not supported on Windows RT.
The Windows soundbanks should be used for Windows 8. No separate platform is provided for Windows 8 in the Wwise project regarding banks.
The above info is available in Unity Integration's documentation as well.