One thing we ought to note is that the Hebrew phrase translated “whoever captures (or wins) souls” is used elsewhere in the OT in places where the sense is “to take life” or “to kill” (e.g., 1 Sam. 24:11; 1 Kings 19:10, 14; Jonah 4:3). It seems clear that the reference here is not in the idea of causing death but in drawing a parallel in the drama and extent of what is happening in the spiritual realm.
And so, this proverb appears to be purposely playing off the usual sense of the phrase to focus on the effect of the fruit of the righteous. The life of the righteous leads not only to blessing for themselves but also provides fruit that “captures souls” in the sense of leading people off the path that ends in death. It is almost certainly referring to idea of evangelism and the matter of preaching and witnessing the truth of the Gospel with the result that, as a result, persons come to know the Lord.