When you activate the map room switch that unlocks the door, it triggers a few stealth elites to be near the entrance. Not that they're really tough, but they can be a real pain in the arse and this can really help save ammo and health.
Well, here's an easier way to take care of them.
You should bring a loaded hog (or at least a gunner) through those trees and up the hill. But when you're near the first pair of hunters, try to keep the hog away from them. Once you progress through those battles leading to the structure, bring the hog in. But make sure it isn't at the bottom of the hallway, as the hunters in the structure can kill them.
Once you kill the hunters, just park the hog behind those crates and activate the switch. Go back to your hog and the elites should fire at you. Once they do, your gunner should really be tearing them up.