If I remember correctly, you only have one shot at actually opening the gates: You have to use a "turn into bug" scroll and go under the gate, kill the guards and then open the gate using the wheel there. However, if you fail and have to load, the gate stays shut for some reason. Or at least, I seem to remember it that way.
Anyway, it's not very important, as you get a teleport rune later on that will take you inside the camp without having to open the door.