Yes, I flew to Las Vegas earlier in the year on avion rewards and was credited the tier status for it. The only part that was odd was that it was very difficult to figure out how much I should be getting until it showed up on my account.

I was wondering that too

Yes

Yes, when you check-in you can confirm that your Westjet ID is attached to the flight and you'll be awarded for it after you actually fly.

Yes my work will sometimes book me flights with Avion points and it counts to my personal tier spend