Not just pawns. They hate the darkness to. Read Ghost Fragment: Fallen talks about a Baron killing hive, and also, if you see the mission where you meet the Queen her fallen are Blue. They belong to the House of Winter. In absence of a Kel or Prime Servitor the Fallen seek any leadership. This makes me think that they are not inherently evil. What makes sense is that the servitors are made by the darkness and they took over the fallen from within, thats why they are the only Fallen enemy with Void.