"Aren't those who are excommunicated unable to obtain spiritual benefits for others???? At least so long as they are excommunicated?"
No laymen who attend SSPX chapels have been declared to be excommunicated nor schismatic, at least by the Church. The Ecclesia Dei Commission has confirmed on numerous occasions that a Catholic can fulfill his Sunday obligation at SSPX chapels. The vast majority of those 1 million rosaries are from the traditionalist laymen.
The priests who accept ordination at the hands of excommunicated bishops may well, by such acceptance, display adherence to the SSPX cult (can one imagine otherwise unless they formally break with SSPX as did the FSSP fathers?) and, if so, demonstrate that they too are excommunicated. We are not Donatist heretics who believe that the sinfulness of the priest vitiates somehow his actual power to say Mass or confect the Eucharist. According to the Vatican, the actual Faithful who attend SSPX Masses may also contribute modestly their share of the expenses. None of this suggests that the Vatican encourages contact with SSPX or its adherents.
Also, when we say the Act of Contrition as part of the Sacrament of Penance, we promise to "avoid the near occasion of sin." Suppose, arguendo, that there were an excommunicated cult of schismatics who effectively teach that the Holy Father need not be obeyed when he directly orders that certain priests not be consecrated as bishops, that the archbishop receiving those orders signs his written agreement to obey that order, that the archbishop in question then communicates with the four priests whom he was ordered NOT to consecrate as bishops, expressing his disagreement with the pope and saying that the Holy See and the Vatican bureaucracies are occupied by "antichrists," is it reasonable to assume that priests willingly associating with such a cult may well, in their preaching and spiritual advice, be that "near occasion of sin" which we promise to avoid every bit as much as we should avoid the confessional of a priest who advises that fornication, adultery, or other sins are nothing to worry about or to confess?
That someone is a layman ought to make it easier to avoid "adherence" to the SSPX cult: 1 sincere confession and penance and re-adherence to the actual Roman Catholic Church and future avoidance of the near occasion of sin and the adherence is cured.
That does not mean that being a layman is a complete defense against being an excommunicated schismatic for "adhering" to the SSPX cult. Ordination is NOT a necessary precondition to adherence to the cult in the sense that one participant in adultery having to be married is a necessary precondition distinguishing adultery from fornication.
The reference to excommunicated was as to one who was and, apparently, is surely excommunicated: the archschismatic du jour Fellay. What those individuals who are NOT excommunicated are doing by way of rosaries or other prayers on behalf of Benedict XVI has nothing whatever to do with the promises of the archschismatic. I pray for the intentions of the Holy Father with every rosary and on other occasions but, trust me, although I am sooooo traditionalist that I actually believe in and obey papal authority as well as attending Tridentine Mass every week, the archschismatic Fellay is in no position whatever to offer any benefit of this Traditionalist Catholic's prayers to or for anyone and he never will be in such a position even if he returns to Holy Mother the Church. Fellay is not a layman. He purported to offer 1 million rosaries of others.
Were the SSPX laity who "adhere" to the SSPX not declared schismatic and excommunicated by John Paul the Great in Ecclesia Dei Afflicta? I was not aware that John Paul the Great distinguished between clerical and lay adherents to the schism. Have you a source for that? [Not a bureaucrat's opinion but a papal opinion of John Paul the Great or of Benedict XVI].
IK believe that is misleading. I will post a link to a letter from Msgr Perl that more acurately characterises the matter