It is not entirely clear that Pietism predated Anabaptism – in as much as Zwingli is considered to be an Anabaptist antecedent, and Dirk Philips is considered an Anabaptist founder, so would any reformer that displayed the key ingredients of the pietist theo-philosophy be by definition worked into the Radical Reformation as an Anabaptist or at least, heavily and perhaps fatally suspected of significant Anabaptist-leanings. Just as the Mennonite and Hutterite Anabaptists built on the traditions of Zwingli, Huss, and the Waldenses, and even, for that matter, on Luther and Calvin, the Pietists represent a distinctive moment in time, separate but probably heavily influenced by Anabaptism – especially the Anabaptist strains from the Netherlands and Danzig.
Most notably, Spener was, and remained, a Lutheran born about 100 years after the death of Menno Simons. Of the Pietist precedents, none shines out more clearly than Johann Arndt. In The Pietist Theologians, Carter Lindberg puts forth a pretty strong case that while Arndt was definitely a contributor to Pietism, he was not in the end a true Pietist and that the honorific of “Father of Pietism” should remain on the faithful shoulders of Spener and his Pia Desiderata. Arguably, both Arndt and Spener contributed significant personal and new content to the shaping of Pietism and peculiar approaches to the combined influences of the Luther Reformation, the Dutch-German Mystical traditions dating back to the Middle Ages, and the spirited Anabaptism that those men saw around them. In fact, we know from his biographical narrative that Arndt was acquainted with and probably influenced by Mennonite neighbors and business connections. Interestingly, his exclamatory exclamation contra his Mennonite neighbor leaves room for being both influenced by the Mennonites as well as sharing a new discovery with them -- that they, the Mennonites, would want to keep such a wonderful things to themselves.