At this moment only Android 4.4.x (KitKat) on tablets is supported. The latest Android 5.0 (Lollipop) is a no-go. In addition older tablets like my Asus ME172v with Android 4.1.x are drop-outs.
It'll be interesting to see which Android versions Microsoft will support when the final version of Office for Android is released. Ok, Android 2.x and 3.x are not on the list. So there are only Android 4.4.x and 5.0 left to support.
In my opinion Microsoft will support both Android 4.4 and 5.0. Why? Simply put they have to. There are so many tablets out there with Android 4.4 inside. Keep in mind 4.4 has Dalvik runtime while 5.0 moved to ART. This can make things complicated.