My comments, or opinion comes from my experience. I've been in a situation where the Pastor take total control of the music ministry and I've been in the situation where the MOM is allowed "freedom."
I've taken a break from the MOM job and now I'm just an organist, but when I was an MOM, me and my pastor used to meet on a regular basis. Actually- myself, along with my staff (all musicians and a choir representitive-like a choir president) would meet and talk about things that happened, where we plan to go next, and get dates for the calendar straight. This where my vision comment came into play. The pastor really didn't mind what we did...as long as it was in decent and in order, it was fine. The choirs did a variety of music and the congregation was very responsive to the music ministry. At the end of every year, myself with the help of a few others would draft a report of the year, and a proposal with goals for the next year for the pastor to read, then we would discuss it in our next meeting. We encouraged some disagreements, but they were worked out and things worked fine. We also had meeting with the whole music ministry every quarter to discuss goals, progress and such.
I was the assistant to the MOM in this next situation. The pastor was a musician, but not a very good one. He could only play in one key, and his ear was defiantly not the greatest. However, he would hire a minister of music, but often he would come in to rehearsal unannounced, and teach songs and such...then expect everyone to know everything by Sunday. After a while, the MOM became confused, and we had a meeting cause everyone really wanted to know what their role was in the ministry. His role for the MOM on paper, and his actions didn't line up...so many got fired, or left.
I say that things work better when the Pastor and the MOM can trust each other and agree by actions. If you hire a talented and annointed MOM, they should trust them to flow in the spirit and do what the Lord tells them.