The major claim against Orientalium Ecclesiarum (OE) has to do with Catholic receive sacraments from the Orthodox or vice versa. The claim is made that outside the Catholic Church there is no salvation or remission of sins (Unam Sanctum) As a result, those outside of the Catholic Church cannot receive sacraments from Catholic preist because they involve the remission of sins, nor can a Catholic receive sacraments from an Orthodox priest. The relevant clauses in OE are #27-30. A list of quotes about saying schematics or heretics cannot receive the sacraments is usually given.
This claim has little standing in the tradition of the Catholic Church. For, example we can take the Donatist errors back in St. Augustine time (300-400 AD). The Donatist’s held that if a priest or bishop betrayed and denied Christ during a persecution then subsequently repented and returned to the Church they would be unable to administer sacraments. The Donatist’s contrary to the Church’s understanding of the sacraments held that the minister’s holiness mattered for the sacraments to be valid and take effect. As a result, if anyone converted from Catholicism to the Donatist church they would re-baptize them if they had been baptized by a clergy who had betrayed the Church then repented. This was a clear error. The sacraments do not depend on the holiness of the minister. (though it can be a grave sin for a priest to administer the sacraments will in grave sin)
Check out this quote from NewAdvent.org (Linked Here) “But from the controversy between St. Augustine and the Donatists in the fourth century and especially from the controversy between St. Stephen and St. Cyprian in the third century, we know that personal holiness or the state of grace in the minister is not a prerequisite for the valid administration of the sacrament. This has been solemnly defined in several general councils including the Council of Trent (Sess VII, can.12, ibid., de bapt., can. 4). The reason is that the sacraments have their efficacy by Divine institution and through the merits of Christ. Unworthy ministers, validly conferring the sacraments, cannot impede the efficacy of signs ordained by Christ to produce grace ex opere operato (cf. St. Thomas, III:64:5, III:64:9). “
So already, at least baptism can be administered by schismatics and/or heretics validly since the beginning of the Church. The Church never re-baptized the Donatist once the returned to the Catholic Church. Hence, we can start to see how Orthodox, like the Donatist, who maintain a valid priesthood can also administer sacraments in certain exceptional cases.
We can see this logic throughout the Church’s history in many ways. For example, Canon 8 in the Ecumenical council of Nicaea, “Concerning those who call themselves Cathari, if they come over to the Catholic and Apostolic Church, the great and holy Synod decrees that they who are ordained shall continue as they are in the clergy…” (Source) (Cathari were Novatianists who had maintained a valid priesthood) The only way Novatianists clergy could maintain their status as clergy if they converted was if the sacraments of ordination was validly (although sinfully) administered to them.
I think we can rest the defense here. What OE is saying is not to receive the sacraments from the Orthodox if a Catholic minister is available but under special salvation orientated situations.
OE #26-27 “Common participation in worship (communicatio in sacris) which harms the unity of the Church or involves formal acceptance of error or the danger of aberration in the faith, of scandal and indifferentism, is forbidden by divine law. On the other hand, pastoral experience shows clearly that, as regards our Eastern brethren, there should be taken into consideration the different cases of individuals, where neither the unity of the Church is hurt nor are verified the dangers that must be avoided, but where the needs of the salvation of souls and their spiritual good are impelling motives. For that reason the Catholic Church has always adopted and now adopts rather a mild policy, offering to all the means of salvation and an example of charity among Christians, through participation in the sacraments and in other sacred functions and things. With this in mind, “lest because of the harshness of our judgment we be an obstacle to those seeking salvation” and in order more and more to promote union with the Eastern Churches separated from us, the Sacred Council lays down the following policy. Without prejudice to the principles noted earlier, Eastern Christians who are in fact separated in good faith from the Catholic Church, if they ask of their own accord and have the right dispositions, may be admitted to the sacraments of Penance, the Eucharist and the Anointing of the Sick. Further, Catholics may ask for these same sacraments from those non-Catholic ministers whose churches possess valid sacraments, as often as necessity or a genuine spiritual benefit recommends such a course and access to a Catholic priest is physically or morally impossible.” (Vatican Translation)
Notice how OE says that common worship which accepts error is forbidden. Then it says that if dangers are avoided and the Orthodox are suitably disposed they may ask sacraments from a Catholic Priest. OE or the Church cannot deny someone who is validly baptized the sacraments unless it means participating in error, but an suitably disposed orthodox would not be trying to promote error at that instance. Then, it says a Catholic may receive the sacraments from an Orthodox priest if necessity requires. The Church cannot deny that the Orthodox have valid priesthood, thus it is sin to receive from them if their is no good reason, but if there is reason, like dying and no Catholic Priest within 100 km then the Church grants you permission. The valid sacraments of the Orthodox make then invisible member of the Church because baptism if valid (regardless of who administered it) makes you part of the Church. Thus, salvation is still only within the Catholic Church as Vatican II clearly proclaims elsewhere in Lumen Gentium. (See our defense of LG)