This is an interesting question, I deal with this on a daily basis. I think that the two roles boil down to responsibility.... In the ministry that is.
I can use my self as an example... I am a drummer, a musician if you will. My responsibility is to play the drums under the direction of the M.O.M. Being the musician, my job is to learn the music that the directors give me, and to display musicianship in terms of knowing my music, being at all events that require me to play, to be submissive to my leadership, and to follow the directions of the M.O.M...
The M.O.M is a little different, well, a lot different. they have to know theory, voices, media, how to play every insturment in their particular church. They have to be able to delegate responsibility, and be accountable for their musicians, and choir members, dancers, stompers, and sound tech people. the MOM has a responsibility to lead worship and ministering to every level of salvation in the church. From the oldest to the youngest, saved and unsaved. The MOM is directly under the pastor, and should be treated with the same amount of respect that the pastor is treated with. They arent merely the director, or head musician. The MOM is responsible for the business aspect as well. Accepting or declining playing/singing at other churches or programs, if the choir is required to pay dues, the MOM ensures that dues are being paid, making sure that the budget for the music ministry is good and in order. And the list may actually go on. They are teachers, advisors, conselors, spiritual warriors in the sense that they have been called by God to complete the task of MINISTER....
I really dont understand how a person could think that the MOM and a musician is the same thing. Because they are NOT. I think that in smaller churches, or rural areas with small congregations, they may not have the means to pay a MOM, so they use who they have, and most times, they get by okay.
All in all, I think that there is a well defined, very obvious difference between the two.....Ray Charles can see it. Why is this even a debate???