As most are aware the US and several other servers Brutal Onslaught is glitched, the NPCs do NOT appear with a weakness symbol and killing them close together DOES NOT trigger the smart ammo. The only way I have been able to advance the commendation is when I joined a European players Team and they were not glitched.
So if you set a mission on hard Brutal Onslaught and can see the symbols PLEASE add me as a friend so I can join you and help. I can help you with any other things you need help with and will give you any drops of mine you want.
Testing if you are glitched:
Set WarrenGate on Hard Brutal Onslaught, look at a mob and if the special weakness symbols appear next to them you are not on a glitched server and can help.
If you are unsure what the symbols look like then set it to Savage Onslaught and you will see them (oblivious once you know what it looks like)