ADT r22 breaks Unity3d ability to export to Android.
Here is a quick fix.
Basically you should use ADT r21, but since you already upgraded to r22 (and assuming you don't want to roll-back), you should use r21 for Unity and r22 (or up) for your other purposes.
It simple, since I created r21 for Unity with everything you need.
1. download and extract it to any folder (just not the original ADT folder).
2. Set unity to work with it (edit, preferences, external tool, Android SDK Location).