If the Necromancer is just about the same as he was last time, I think they'd make a pretty deadly team.
Necromancer protects them both with his army, while the WD keeps the Necro with fresh supply of corpses and his mass murder abilities just wipes out whatever is busy being occupied by the skeletons. nothing would ever reach them.
Not sure how summons would fair agaisnt bosses in this game though. All the summons get raped and the Necromancer curses and hides behind a wall while the WD gets killed while spitting leaves at Diablo or whoever, cause he has terrible back problems and can't run away

All the while the Necromancer is running around screaming Help, Help Me
