Have reached two conclusions:
1) Zazu should be evil.
2) Scar is silly. The hyenas are not his friends. They are his minions; to be used and cast aside. Therefore keeping his promise to them is unnecessary. Then everything would continue spiffy, and everyone would loff him. If the lions could keep the hyenas out before, they can keep them out if Scar's their king, even if Scar promised them spiffiness.