Lubavitchers marry only within Chabad or, especially in EY, France and Canada a generation ago, to graduates of Chabad girls’ schools who may have their own (usually North African or Yemeni) minhagim but who are familiar with Chabad and willing to change. Even 2 generations ago, it was not completely unheard of for a Chabad bochur from Russia to marry a girl whose parents came from Yemen.
Ger marries only Ger, vehamayvin yavin. It is a tough life for someone from outside to get accustomed to.
Satmar and Pupa are meshadech to one another. Smaller chassidus’n are meshadech to the ones most similar to them. Rebbeish families marry into other rebbeish families – the Rebbeim of Satmar, Bobov, Belz, Vizhnitz and Lubavitch are all related through Reb Aron by marriage (all but Belz would be related to his children by blood). The Twerskis of Milwaukee, BP, Pennsylvania etc (Hornestipol) are all related to the Bobover rebbeim as well. I think the rule in Skvere is that only men who went through their system can live in NS, but a kallah from outside is welcome. Please check me on that.
The kallah always takes on her new husband’s minhagim (which I think is halacha).
Oh, and Creedmoor just does things Reverend Moon style – reams of marriage licenses followed by divorces depending on which benefits programs the phantom couple are registered for.