As the other posters have pointed out, it works OK but it's slow. The iPad charger has a 2 amp current capability and can charge the iPad much faster than a normal USB port on a computer or an iPod charger. If you connect it to your PC USB port, you'll typically see the iPad report 'Not charging' because the charge rate is so slow. So it's advisable, for the fastest charge, to always use the supplied iPad charger but, for sure, you won't do any harm by connecting it to the iPod charger.
Also, as the other poster suggested, you can charge the iPod with the iPad charger. Although the iPad charger has a much higher current capability it won't 'force feed' the iPod, which will simply take the current from the iPad charger that it needs - no more.
Tim