By the way, just snipe the Rocket Officers First, so they don't bother you with theyr missiles. After shooting, you will hear: "Let's get out of here"

Then, two engineers will start to run. At first, they will run towards the left, and then turn behind the buggy and run along the ridge all the way to the right. Just shoot them when they turn, as the buggy shouldn't be able to hit you. After shooting them, two more will start running, repeat the prosess twice and you should have killed all 6 engineers.

And theres no real reason for killing them sice no bonus is awarded (I think)