Are Anabaptists' re-baptisms really conditional baptisms? Are Anabaptists' re-baptisms really conditional baptisms? By "conditional baptism" I mean one whose formula is something like: "If you are not baptized, I baptize thee… etc."

In other words: Do Anabaptists really accept two valid baptisms per person, or are their re-baptisms conditional on whether the first one validly occurred or not?

If so, does this tradition continue among any of the traditions descended from Anabaptist roots?
No, they are not.

Present day Anabaptist baptisms are not phrased in any way conditionally. Nor are they considered 'rebaptisms'. Conditional baptism is used only when there is uncertainty about whether someone has been baptised before or not. This is extremely rare in Anabaptist circles, because in their view valid baptism can only be performed on someone of an age to understand it. A person almost always knows whether they have been baptised as an adult. (It's more common with a denomination that admits infant baptism, because someone might have been baptised when they are too young to remember).