Well, this is an odd and kludgy fix... only thing I can find that allows the integration to work correctly and not give an error whether EssentialsChat is present or not

src/com/earth2me/essentials/chat/IEssentialsChatListener.java

@@ -0,0 +1,12 @@
+package com.earth2me.essentials.chat;
+
+import org.bukkit.entity.Player;
+import org.bukkit.event.player.PlayerChatEvent;
+
+
+public interface IEssentialsChatListener
+{
+	boolean shouldHandleThisChat(PlayerChatEvent event);
+
+	String modifyMessage(PlayerChatEvent event, Player target, String message);
+}