Vien is of Oberlander background. The Oberlander community though, has changed over the years. Unterlanders (Chasidishe Hungarians, Unterland being the opposite of Oberland) came in to the kehillah. Chasidishe Rabbonim were hired, who at times tried to make things more Chasidish. Some of the Oberlander (perhaps as a reaction to the above) joined other Ashkenazishe groups such as Yeshivish, Chasidish, and Modern Orthodox.
A few years ago the Williamsburg branch changed to nusach Sfard. But that wasn’t because all the old Oberlanders converted, rather that there were hardly any left in that neighborhood, and the Viener Rav/Rebbe had brought Chasidishe in. The main Vien in BP still davens Ashkenaz.
To say that all the Oberlander kids wear shtreimels is not true. You can find Ashkenaz Oberlander kids in places like Lakewood and elsewhere.