The group in question here is not a true militia as mentioned in the Constitution. However, it is a legal body and can be utilized as stated if accepted by the local sheriff, which it does seem to be. The militia has to be organized and commanded through the State AG as stated in the AZ state code. I thought that the OP meant an actual state activated militia as meant by the Second Amendment to the Constitution of the US.

This group, if authorized by the County sheriff , constitutes a legal posse, which can be formed by any county for a specific purpose like this.