Check if the current selection is in the Unity3D Hierarchy Panel

HierarchyUtils.cs

using UnityEngine;
using UnityEditor;

public class HierarchyUtils {

	/// <summary>
	/// Determines if the current selection in the Hierarchy view.
	/// </summary>
	/// <returns><c>true</c> if is selection in hierarchy; otherwise, <c>false</c>.</returns>
	private static bool IsSelectionInHierarchy() {
		Object[] objs = Selection.objects;
		if(objs.Length == 0) return false;

		GameObject go;
		foreach(Object obj in objs) {
			go = obj as GameObject;
			if(go == null) return false;
			if(!IsInScene(go)) return false;
		}
		return true;
	}

	/// <summary>
	/// Determines if a GameObject is in the Scene.
	/// </summary>
	/// <returns><c>true</c> if the GameObject is in the Scene view; otherwise, <c>false</c>.</returns>
	/// <param name="go">The Game Object.</param>
	private static bool IsInScene(GameObject go) {
		return go != null && (PrefabUtility.GetPrefabType(go).ToString().EndsWith("Instance") || PrefabUtility.GetPrefabType(go) == PrefabType.None);
	}
}