But their geography, culture and demographics are similar, let's say, so Orre probably is bording Unova, or are next to each other, so your statement that the Desert Resort contains Pokemon inhabiting Orre makes a lot of sense.
Particularly I always thought that regions like Orre, Fiore, etc .. are smaller than the main games regions .
Moreover, there isn't unique-typical Pokemon there, I mean, their wildlife are nothing special.