A. No. The difference is that the extra priests are actually concelebrating. The extra deacons are vested, but they are not performing liturgical actions in the same way as the deacons ministering in the sanctuary.
Q: When there are more than two deacons at a Mass at the cathedral, what postures do they take during the eucharistic prayer? The two deacons at the altar kneel from the epiclesis to the memorial acclamation, but what about the others? Do they kneel from the Sanctus to the Amen as the people do?
A: There is no legislation on this. Some dioceses have expressed a preference. Others have not.
Personally, I think it’s better for deacons in pews away from the sanctuary to assume the postures of the rest of the assembly. GIRM 43 refers to what postures “the faithful” should take. Extra deacons are more like members of the faithful than ministers of the mass.
Q. Would we say the same thing about additional vested priests at the Liturgy of the Eucharist if they were seated with the assembly?