Mmmm, as planet of Hats says a Medieval success seems unfeasible, unless they turn into something like the Franciscans. It would not be a denomination, but a religious order, so a bit different than what you ask.
A possibility would be a much stronger Duchy of Savoy that comes to control Genoa and somehow acquires a colony in the New World and uses the Waldensian minority to populate it. It is not going to be anything more than a footnote in history in most plausible scenarios though...
Or they survive as iotl until the Reformation, which somehow spreads more to Italy, leading one of the Dukes of Savoy (or Montferrat) to adopt a Calvinist-influenced form of waldensianism (something like today's Chiesa Evangelica Valdese) as its State Religion (they were formally part of the HRE, weren't they? You need to dreastically weaken the Roman Catholic Church however, which by itself would bring much more significant butterflies than a Waldensian Piedmont.