no problem finding shidduchim amongs other Lubavitch B’T’s
That’s exactly it. They’re not accepted as part off the “reall” thing. It dosent seem as if the person the OP is talking about is seeking a new “BT” culturer. In other chasidessen they’ll at least be completly accepted, just shiduchim when their liniage is researched, will be difficult.
In the Yeshivish world I can tell you of two cases I’m personally familiar with. One boy who became Frum at 15.. married a Rosh Yeshivas daughter (and that RY carries a world famous family name). Another family, where the parents became Frum once married, their daughter married a RY’s son. I know both cases from close by