Gregory,
Be very careful with this subject please, there are people on this forum who has been baptized in his care.
It is customary and tradition that if one suspects a bishop is a heretic it is only proven by asking / requiring him to make a confession of faith. Until then there is nothing, unless the heresy is brazen and clear. I don't think anyone here is in a position to start speculating about what was known and not known, if there was anything at all at the time! It seems the ROAC has had a healthy enough response to a problem.
And I don't think there is a problem with baptizing a Cyprianite. I don't think any "traditional" synod would do this however, they would most likely be received by Holy Chrismation.
I don't beleive this was the synod at issue with Met. Valentinos, I believe it was a Matthewite that was re-baptized. Here the issue seems to be, unlike the Cyprianites, there is no difference in faith between them, so a lack of communion does not nessesarily mean a lack of the Mysteries. This is of course problematic, but so are most things through history in Orthodoxy.
And I thought I would also mention, the Sixth Ecumenical Council was also a big fan of St. Cyprians (ie. Orthodox) understanding of baptism. We are taught as all the Holy Father say, THERE ARE NO MYSTERIES OUTSIDE THE CHURCH.