Status Update (1)
@Avarre: Jade Owls seem to be a fixed uncommon quality, Sapphire Cubs can come in any of the 4 qualities, so that includes rare.
Additional Comments by Date (2)
Just found 4 up at the same time. So it's possible to have more than 1 up at the same time. Of course, no rare yet. But for those hunting them, there's more than 1 spawn. All north of Greenwarden's though.