AoM is a really really great world book in general for Dragonlance. You don't need it, persay, as KoT does an absolutly excellent job of making sure that the module is completely standalone, hitting all cultures, flora and fauna that you're likely to meet up with. Admittedly, it might help a bit with the Kender Nightstalker NPC, but really, he's low enough level that you can fake it.
personally, i really enjoy AoM, but for key of destiny, all you need is the DLCS (the mini adventure in the back, _The Sylvan Key_, is the prologue to Key of Destiny).