Personally I'd slot both. There's room because you have Soul Extraction as a slot mule for the pet IOs. The -Res is even better when teaming.
On sets that have a mule (Gang War), can you slot all 6 of the pet aura IOs or do some of them need to be on an active pet to reap the benefit? In particular, some of them are described as "bonus aura". Does this aura live on the player or on the pet? If so does the benefit only show up when Gang War is active?
Aura IOs are always active.
As to slotting then all in gang war, I'd recommend against it, as gang war is actually useful when slotted to hit, damage, and Recharge. Perhaps 3 aura IOs then framkenslot the remaining three slots for accd/dam in Gang War. Distribute other three aura UOs in your other pets. There might be a better way to do it, I'm not a thugs guy.
Gangwar is a strange power in it's good out of the box but they do die quick and will never be high damage. I personally would 6 slot your aura stuff in there unless your going for double gangwar or something.