Vos wouldn't stand a chance against Asajj. He's good, but unless you want to say that he could match Obi-Wan or Anakin blow for blow, he's not walking out of this alive.
Luminara has a good shot at Ventress, due in greater part to her style of fighting than anything. She probably wouldn't need to give as much ground as say, Obi-Wan, due to her amazing dexterity. She'd weave through the acolyte's attacks, and find an easy opening.