Is matched betting possible in Western Australia?

Definitely. In fact, there are very few restrictions for people in W.A..

The biggest issue that you will have is that TAB will not give you bonus bets. This is because TAB do not operate in Western Australia (W.A. has TABTouch instead).

Other than that you will find that almost every bookie pays bonuses to W.A. so you will be able to make a healthy profit each month.