public class Unit : MonoBehaviour {

	public event System.Action OnSpawn;
	//public event System.Action OnDeath;

	void Start () {
		if (OnSpawn != null)
			OnSpawn ();
	}
}

public class Spawner : MonoBehaviour {
	UnitManager unitManager;

	void Start () {
		unitManager = FindObjectOfType<UnitManager>();
	}
	public void SpawnAxeman(int amount)
	{
		Unit spawned = Instantiate(AxemanPrefab, spawnPosition.position, spawnPosition.rotation)as Unit;
		spawned.OnSpawn += unitManager.OnUnitSpawn;		//unit manager needs to listen for the spawn event from the unit.
	}
}

public class UnitManager : MonoBehaviour {
	public void OnUnitSpawn()		//listens to the event of units spawning
	{
		Debug.Log ("event sys working  i know unit spawned, but no ref!");
	}
}