He definitely needs his zeta to function correctly. I've been running zzEP/thrawn/zSion/Nihilus/Vader ( all g12+ except 5* maxed Sion) for a good bit now, and without his zeta he almost always died before he got to Hatred. I've tried both standard Nightmare with a g12+1 Sith Trooper, and non-zeta thrawn, and the thrawn config works much more reliably, especially against JTR squads. He needs as much speed as possible, at least +100 to start, and stacking protection on the triangle, cross, and circle to make sure he can take any counters or assist chains from cls and JTR. A speed set is best to hurry him to Hatred ASAP, if you have enough to spare after modding Vader and nihilus as fast as possible.