We know that Summorum Pontificum allows a priest to say the Mass according to the 1962 Missale Romanum and to perform other sacraments pursuant to the appropriate edition of the Rituale Romanum. But what about deacons? Does Summorum Pontificum apply to deacons? What can a deacon do in the Extraordinary Form?
The answer to the first question is “yes.” Writing in 2008, the Pontifical Commission Ecclesia Dei announced:
The Motu Proprio Summorum Pontificum, just as the Motu Proprio Ecclesia Dei, presupposes that any deacons, transitional or permanent, may function as deacons in the Mass according to the 1962 Roman Missal, provided, of course, that they are familiar with the rites and can function with sufficient ease. The local Ordinary can not impede a deacon in good standing from functioning as a deacon in the extraordinary form of the Roman Rite provided that the deacon is qualified.
As for the second question, deacons obviously have liturgical roles to play in Solemn Masses. Deacons are also permitted to impart some blessings and to perform baptisms using previously blessed water and salt.
Likewise, it appears that a deacon can distribute Holy Communion at Mass in the Extraordinary Form. Although the rubrics seem to say that priests alone distribute Holy Communion, the 1917 Code made deacons extraordinary ministers of Holy Communion and required the bishop’s or pastor’s permission to perform that function, the 1983 Code makes the deacon an ordinary minister of Holy Communion. Thus, since the deacon’s role in this regard was previously amenable to control by the Code of Canon law, apart from the rubrics themselves, the sensible conclusion would be that it remains so under Summorum Pontificum; thus, a deacon may distribute Holy Communion during Mass in the Extraordinary Form, and may (it appears) do so without special authorization.
 Letter of Pontifical Commission Ecclesia Dei to unknown individual (2008), available at http://wdtprs.com/blog/2008/02/pced-clarifies-service-of-deacons-in-the-tlm.
 See, e.g., Fr. Daniel Gill, Deacons and Summorum Pontificum, Servatis Servandis (May 1, 2014), https://dcgb7f.wordpress.com/2014/05/01/deacons-and-summorum-pontificum (citing, inter alia, Sacred Congregation of Rites, Order of Baptism of Children ¶ 27, in Rituale Romanum (1952)).
 See Gill, supra note 2.