Fr. Feeney was opposing the outright DENIAL of the dogma of EENS. This is what was occurring in Boston at the time. The Holy Office letter was not condemning Fr. Feeney...it was explaining the correct understanding of the dogma...which was at odds with both Fr. Feeney AND those who were denying the dogma or obscuring it's meaning.
Sure, it was advancing the heresy of implicit faith, which Pius XII (a progressive pope, according to most observers) also advanced, which paved the way for Vatican II. Father Feeney was never condemned. We all know this. As a matter of fact, even JPII did not condemn Feeneyism, but I do not have the docuмent where he (JP II) cites the three de fide pronouncements (Lateran, Unam Sanctam, Florence) but he does list the Denzinger references to them. I believe in both BoD and BoB, but I do not go beyond the limits that the Church has infallibly set, in spite of what the post-conciliar popes, SSPX, etc. are saying.
No, I don't think so. The heresy being advanced was an invisible membership in the Church in a much broader sense. Vatican II broadened the Church to include all people and all religions in an "imperfect way". Imperfect communion has to do with the SECT...not any individual.
The visibility of the Church requires a visible membership.