I 3starred CT3 on this most recent run of PoP. Took several attempts to develop the winning strategy. Previously I didn't bother, but now that we can sim ABs, I only had to win once.
Team was Palp lead, Vader, SEE, Nihilus, Dooku. All R7 except for Nihilus, who is R3. Potency>>>>>>speed on Palp, you wanna land those stuns and shocks. 260 speed is perfectly fine on Palp. As much speed as you can get on Nihilus, he uses Annihilate on wave 7 and has to recharge it for wave 8.
1) SEE Link priority on Jedi Knight Guardian and the two-saber one who stealths. Both can do a lot of dmg on the AOE, Guardian also has ability block.
2) Vader is just there for dots and doing MM-->mass ability block. Culling Blade is absolutely useless because it does no damge and you'll actually clear all the debuffs off an enemy
3) beware of key enemies: Aayla Secura (stun machine); JKA (powerful AOE, healing/buff immunity); Rex (one well-placed Rexecute can end a 3star run); Kit Fisto (his AOE can wipe out squishier Sith like Dooku/Palp if you go into wave 6 low on health/prot); GMY (obvious reasons); GK (mass assist can kill your guys, ability block is important); QGJ (calls assists, grants offense up); Mace (those exposes can sneak a kill past you if you're careless)
4) Nihilus Annihilate targets: JKA on wave 4 (get rid of that AOE, slow down Rex); Luminara on wave 7 (just to debuff the enemy); GMY on wave 8 (everything rests on this, GMY will go nuts if you don't control him right away)
5) have SEE ult ready to go on wave 7, enter wave 8 already in ult form to link GK and QGJ right away, GMY is Nihilus' job; be aware of the ult charge condition for SEE outside of the leader slot--Deceived enemies need to use an ability to give 2% ult charge, which means that if their turn is used up to exit stun or die from dots, they don't give any ult charge
6) no Sith with a passive stealth gain ability--GMY will steal stealth on his AOE and then when Nihilus' turn comes up, you can't Annihilate even if GK isn't taunting; I never used Dooku's 2nd special in the whole run
7) do not trigger taunt on GK in wave 8 until Nihilus goes and Annhilites GMY; only hit GK, no Vader MM, no AOE until GMY is dead