Like many, I responded with shock and disgust when I heard of this diabolical means of silencing good priests. I had always understood that the seal of confession is absolute, but it made me wonder if a priest who hears such a confession was precluded from doing anything. For example, obviously a priest who hears a confession cannot go to his bishop and say "Bishop, Monsignor Joe confessed to me that he is abusing seminarians," for that would break the seal. But, could not the same priest say, "Bishop, I can't go in to specifics but I have reasons to suspect that Monsignor Joe is unfit for the priesthood and should be investigated"? Such an approach would not reveal that Monsignor Joe had confessed to the priest, nor would it reveal the content of what had been said.
I posed this question to a priest friend of mine and he enlightened me on an aspect of the seal of confession I had been hitherto unaware. He told me that the seal of confession does not merely preclude a priest from disclosing what is revealed in confession, but that the priest cannot take any action based on what he hears in confession.
For example, if Person A confesses to a priest that he is in the custom of habitually stealing from his employers, and then later Person B tells the priest he is planning on hiring Person A, the priest cannot say, "I wouldn't do that if I were you." Even though he's not revealing anything about what was confessed, he is taking positive action based on what he learned through confession, and this violates the seal. He cannot use knowledge he has obtained during confession in any way, not only by word but even by action.
The priest I consulted about this referred me to the following excerpt from Fr. Prummer's 1957 Handbook of Moral Theology:
706. THEREFORE IT IS FORBIDDEN TO USE KNOWLEDGE DERIVED FROM HEARING CONFESSIONS:1. even for the greatest spiritual or temporal good. Thus, for example, a confessor is prevented from confessing his own sin, when its revelation would violate the seal; he cannot take to flight or omit to say Mass is he knows from confession alone that his life is threatened or the wine is poisoned; he cannot dismiss a servant whom he knows from confession to be a thief or to be with child;2. for the public good. Consequently a priest is not allowed to disclose the name of a penitent whom he knows from confession is about to betray his country or to murder some innocent person;3. for the good of religion. Consequently a priest cannot expose a penitent he knows from confession will receive Holy Communion unworthily; he is obliged even to administer Holy Communion to such a person if the latter asks for it.
Handbook of Moral Theology by Dominic M. Prummer, O.P. P.J. Kennedy & Sons, New York. 1957
This is why an abuser priest confessing to an orthodox priest is so diabolical; it not only binds him to silence, but to total inactivity.
That being said, the priest I discussed this with said he did not believe the rumors about deviant priests doing this. I can't speak to that; I only know what I have heard.