The Supreme Court in 1871 had nine Yankees on it, 5 selected by Lincoln himself.
That's because all the southern justices had resigned and run off to join the rebellion. I imagine that they had visions of helping establish the confederate supreme court. Boy, weren't they surprised!
Regardless, Virginia v West Virginia was a 7 to 3 decision, and by agreeing to hear it the court recognized West Virginia's status as a state.