Do we know how many bishops attending the Council of Nicaea were actual victims of the Roman perscutions?
We will certainly never know how many bishops who participated in the Council of Nicaea were somehow persecuted in the last of the Roman perscutions. All we really know is that some of them had suffered by the hands of the Roman persecutors in one why or another.
Most of the bishops present were Greeks; among the Latins we know only Hosius of Cordova, Cecilian of Carthage, Mark of Calabria, Nicasius of Dijon, Donnus of Stridon in Pannonia, and the two Roman priests, Victor and Vincentius, representing the pope. The assembly numbered among its most famous members St. Alexander of Alexandria, Eustathius of Antioch, Macarius of Jerusalem, Eusebius of Nicomedia, Eusebius of Caesarea, and Nicholas of Myra. Some had suffered during the last persecution; others were poorly enough acquainted with Christian theology. Among the members was a young deacon, Athanasius of Alexandria, for whom this Council was to be the prelude to a life of conflict and of glory. - The First Council of Nicaea
St. Nicholas of Myra Was put into prison during the persecution of Diocletian, he was released after the accession of Constantine.
Bishop of Myra in Lycia; died 6 December, 345 or 352. Though he is one of the most popular saints in the Greek as well as the Latin Church, there is scarcely anything historically certain about him except that he was Bishop of Myra in the fourth century.
Some of the main points in his legend are as follows: He was born at Parara, a city of Lycia in Asia Minor; in his youth he made a pilgrimage to Egypt and Palestine; shortly after his return he became Bishop of Myra; cast into prison during the persecution of Diocletian, he was released after the accession of Constantine, and was present at the Council of Nicaea. - St. Nicholas of Myra
St. Paphnutius Suffered persecution and also attended the Council of Nicaea.
The most celebrated personage of this name was bishop of a city in the Upper Thebaid in the early fourth century, and one of the most interesting members of the Council of Nicæa (325). He suffered mutilation of the left knee and the loss of his right eye for the Faith under the Emperor Maximinus (308-13), and was subsequently condemned to the mines. At Nicæa he was greatly honoured by Constantine the Great, who, according to Socrates (Church History I.11), used often to send for the good old confessor and kiss the place whence the eye had been torn out. He took a prominent, perhaps a decisive, part in the debate at the First Œcumenical Council on the subject of the celibacy of the clergy. It seems that most of the bishops present were disposed to follow the precedent of the Council of Elvira (can. xxxiii) prohibiting conjugal relations to those bishops, priests, deacons, and, according to Sozomen, sub-deacons, who were married before ordination. Paphnutius earnestly entreated his fellow-bishops not to impose this obligation on the orders of the clergy concerned. He proposed, in accordance "with the ancient tradition of the Church", that only those who were celibates at the time of ordination should continue to observe continence, but, on the other hand, that "none should be separated from her, to whom, while yet unordained, he had been united". The great veneration in which he was held, and the well known fact that he had himself observed the strictest chastity all his life, gave weight to his proposal, which was unanimously adopted. The council left it to the discretion of the married clergy to continue or discontinue their marital relations. Paphnutius was present at the Synod of Tyre (335). - Paphnutius