In our parish, (the diocese Cathedral) We have MC’s for ordinations, All Mass’s during Holy Week, Chrism Mass, and any Mass (except daily Mass) when the Bishop is present. When our Seminarians serve as MC’s they wear cassock and surplice, when a deacon MC’s they are fully vested with stole and dalmatic, when a priest MC’s, he wears an alb and cincture. I asked one time why the priest doesn’t vest, and the answer was, because he is not participating as a priest during the Mass. Since priests concelebrate, if he was vested with stole and chasuble, he would be concelebrating and not MC’ing. Deacons can be fully vested since they only assist and do not concelebrate.