Technically, rayquaza should be in the ozone layer, which doesn't necessarily mean hoenn specifically. Though, who said there isn't more than one rayquaza.
possible but who knows rayquaza might be heading to another region, just because its a hoenn pokemon doesn't mean that iris should directly head to hoenn.
Probably.
Is there any dragon-ish thing in Hoenn?
She could request to study under Drake of the Hoenn Elite 4. Then there would obviously be myths/legends she could learn about, regarding Rayquaza, Latias and Latios.. Plus there's a large amount of Dragon Tamers for her to battle and learn from..