Well, given that the Catholic Church did nothing to stop forced mass conversions of Orthodox Serbs in fascist puppet-state of Croatia (1941-1945), one is led to believe that this was indeed the teaching of the Catholic Church. I would like to think otherwise, but for the imprimatur to make such an oversight just seems a little too naïve.
By the way, Petrosius, what was the official teaching of the Catholic Church vis-a-vis the Eastern Orthodox Church in the 1930's?
Those ordained by schismatic bishops, who have been otherwise duly ordained, the due form having been observed, receive, indeed, ordination, but not jurisdiction.
--Pope Clement VIII, Instruction concerning the rites of the Italo-Greeks (1595), D1087.
Can. 2372. He who presumes to receive orders from one excommunicated or suspended or interdicted after a declaratory or condemnatory sentence, or from a notorious apostate, heretic, or schismatic, ipso facto contracts a suspension a divinis, reserved to the Apostolic See; however he who should be ordained in good faith by any of them lacks the exercise of the order so received until he shall be dispensed.
--Code of Canon Law (1917).
[Note: The implication is that such ordinations are valid.]
Every validly consecrated bishop, including heretical, schismatic, simonistic or excommunicated bishops, can validly dispense the Sacrament of Order, provided that he has the requisite intention, and follows the essential external rite (sent. cert.).
--Ludwig Ott, Fundamentals of Catholic Dogma (1955), p. 458.