How to play iTween event on all GameObjects tagged "example"

Well, there's a few ways you could go about doing this. The method that you are referring to is at the following link:

http://docs.unity3d.com/Documentation/ScriptReference/GameObject.FindGameObjectsWithTag.html

 GameObject[] shardArray = GameObject.FindGameObjectsWithTag("MonolithicShard");
 
 for( int i = 0; i < shardArray.Length; i++ )
     shardArray[i].SendMessage("yourTweenMethodName",SendMessageOptions.DontRequireReciever);

Or, if your MonolithicShard's have their own Script attached, lets say the class name is MonolithicShard, you could do:

 MonoLithicShard[] shardArray = Object.FindObjectsOfType(typeof(MonoLithicShard)) as MonoLithicShard;
 
 for( int i = 0; i < shardArray.Length; i++ )
     shardArray[i].yourTweenMethodName;

But, but these methods are relatively slow. FindObjectsOfType is quite a few times slower than the tag method, but in turn you're calling methods directly on the references of the scripts rather than using SendMessage, which is slow too. Your best bet would be to use delegates and events, and subscribe to the event of the trigger.

So, on your object that needs to announce the trigger:

 public delegate void ShardTweenHandler(GameObject hitGO);
 public static ShardTweenHandler onTrigger;

 void OnTriggerEnter( Collider other )
 {
      if( onTrigger != null )
          onTrigger( other.gameObject );
 }

To subscribe to the event from your mono lithic shard scripts, you would do:

 void OnEnable() { ClassNameWithEventInside.onTrigger += onTrigger; }
 void OnDisable() { ClassNameWithEventInside.onTrigger -= onTrigger; }
 
 void onTrigger( GameObject hitGO )
 {
     // you can have your iTween in here
 }

For a quick tutorial on delegates and events:

http://www.youtube.com/watch?v=N2zdwKIsXJs