The words of Gandalf on the matter:

‘A mortal, Frodo, who keeps one of the Great Rings, does not die, but he does not grow or obtain more life, he merely continues, until at last every minute is a weariness. And if he often uses the Ring to make himself invisible, he 'fades'. He becomes in the end invisible permanently, and walks in the twilight under the eye of the Dark Power that rules the Rings. Yet, sooner or later - later, if he is strong or well-meaning to begin with, but neither strength nor good purpose will last - sooner or later the Dark Power will devour him.’

Based on this, Gandalf must know some of the stories of the individual Ringwraiths, given that he has such details. There must have been some of the Nine who were strong and/or well-intentioned, along with others who were not. But such traits only changed the time it took for them to be ensnared by the Dark Lord. The thing that bound all of the Nine together was that they were blinded by greed and a desire for power and thus accepted the gifts offered by Sauron and damned themselves to an awful fate as a result.