Lover of Truth: Of course people in those sects you named would not be saved because of their religion or by it but due to their sincerity of heart.
This is heresy or at least proximate to heresy. They would be saved because of explicit faith in Jesus Christ, which, I am claiming, they could receive at the moment of death in the fullness of Christian revelation, which they could, of course, accept or reject. I suppose that it would be akin to some sort of Near-Death experience. If a Buddhist goes to Heaven, it will be a Christian Heaven that he/she finds himself/herself in, and he/she will be worshiping, for all Eternity, the One and Only Son of God. Right?
It is completely conceivable that the One and Triune God being infinite, uncaused, omniscience, omnipotent, and omnipresent could insure that such non-Catholics whom He was going to offer salutary repentance would receive the Sacrament of Baptism during their infancies. To say otherwise would be to deny the attributes of God. If you accept the creation of the Universe ex nihilo, then you must accept the possibility of God doing this, or at least His capability in doing it.