“RS 128. Holy Mass and other liturgical celebrations, which are acts of Christ and of the people of God hierarchically constituted, are ordered in such a way that the sacred ministers and the lay faithful manifestly take part in them each according to his own condition. It is preferable therefore that Priests who are present at a Eucharistic Celebration, unless excused for a good reason, should as a rule exercise the office proper to their Order and thus take part as concelebrants, wearing the sacred vestments. Otherwise, they wear their proper choir dress or a surplice over a cassock. It is not fitting, except in rare and exceptional cases and with reasonable cause, for them to participate at Mass, as regards to externals, in the manner of the lay faithful.”
I think this only applies to priests and of course, bishops. If deacons were to be included I think they would have continued the use of “sacred ministers” instead to transitioning to “Priests.” I don’t think it would be bad for deacons to vest in choir, but I don’t believe it is required as least per the above paragraph.