They are, and they aren't. If 'anabaptism' is defined solely on the basis of the word's etymological meaning ("re-baptize"), then yes, the Munsterites were anabaptists. But I also wonder if that term was ever actually used of them by the Dutch and Spanish over-lords who controlled that part of the Low Countries during that period, because the common Dutch term was a different one, one meaning "baptism-minded". But perhaps the question is the same, regardless of the answer to that question. But as Ernie points out, that is only one part of what is meant by the term "anabaptism" (whether you capitalize it or not, I think), both historically, and currently. The fact that they were not accepted by others of the believer's baptism persuasion at that time is, I think, telling.
Again, the question comes back to "Who gets to define a person or group?". There are people now who define themselves as "Amish" who are not accepted as such by any other Amish group. People also often refer to a certain very conservative group in Ukraine as "Ukrainian Amish", but they do not have, nor have they ever had, any connection to or influence from any Amish group or person. Are they Amish? No, they are not, even though Amish here in the States like to refer to them as such, all because they do not drive vehicles. That is a very narrow definition of what it means to be 'Amish'. Some Amishmen I used to work with in a tractor implement manufacturing operation used this single deliminator to determine if a person is Amish or not - "If you drive vehicles, you are not Amish." They were using this determiner to say that the Beachy Amish-Mennonites are not Amish at all, even though they claim to be, and are similar to both New & Old Order Amish in many other ways. (I told them that the Banawa were "more Amish" than they, because they
walk everywhere.....
)
Congregation: Gospel Haven Mennonite Fellowship, Benton, Ohio (Holmes Co.) a split from Beachy-Amish Mennonite.
Personal heritage & general theological viewpoint: conservative Mennonite Brethren.