As per the rules of the Kaggath, Kreia also shouldn't be able to hide...
She's not really hiding. She's using her weapons and resources to their fullest. It's a part of her character to wait for her enemy. She's a plotter.
Revan is aggressive and would attack. But if you want to go on about how unfair such an engagement is, go ahead. We'll wait for Beni to announce the victor.
Edit: And there's nothing in the rules about "no hiding". So Traya can sit at Malachor all she wants. She's not breaking any rules and its in her character to lurk in the shadows and manipulate things.