Several things come to mind, Chicken Obsessed:
Firstly: no, emus are not naturally ornery. I strongly suspect that the ornery ones you read about are what I call 'paddock-emus' left somewhere in some paddock with nothing but food and water and a fence. You'd be ornery too. In the wild unless cornered, in which case they are highly dangerous they will generally flee. (They are curious though, and I hear that they will approach a tethered dog.)
Secondly, bear in mind that you have two choices: one, secure a grown emu from someone in the States. It will be a chick, in which case you got to raise it ornery; and I'm not sure how you'd do that . . . Two, you secure a grown emu, in which case you need to somehow . . . umm . . . pre-measure its orneriness. That is, having been raised in the States, it will probably be a pet.
Finally, a more serious issue: I have had a number of conversations here about fights between dogs and emus. BYC is a forum for bird lovers, which is why I'm here; but in My Real World, here in Oz, people shoot, poison, and run down emus, on an industrial basis, with glee. My point is that I don't think that pitting a dog against an emu is ethical. Emu lovers might say that an emu will likely win. Dog lovers boast that their dog will gut an emu alive in three seconds I'm being serious here. It's quite likely that an emu will be horribly injured in a fight with a dog. Nil-all draw perhaps.
I hope I haven't offended.
Supreme Emu
Rocky Gully, Western Australia