No, Vettori is not an Aussie - he's a Kiwi (from New Zealand). I'm not finding any information on him coming to the Devils - where did you read this? It doesn't make sense to me given that he's doing so well for New Zealand.
Vettori is the captain of the New Zealand team. He is an excellent player on an outstanding team. I haven't found any information on him leaving New Zealand and, personally, can't think of any reason he would.
Daniel Vettori really seems to have a good thing going right now and, like batgirl, I don't see any reason for him to make any changes at this time. However, in the world of sports you never know what might happen. There are a lot of behind the scenes things going on that the fans never see.
I haven't seen anything about Vettori making a switch. Perhaps the original poster could put a link here to where he originally found that information? I think perhaps you misunderstood something though as there would be something to show up in a Google search about it and I can't find anything to support this.
I am still not sure about the Oz/Kiwi mixup but I have found out some things about him since doing a little more digging:
- scored 3,000 Test runs
- had a crazy back injury (I am surprised he can still play)
- theres an biography of him out that I must have missed, most times I catch these things.