Here is a link to the 2010/2011 Subaru Web site detailing their iPod and USB port option.
iPod & Media Interface | Subaru Electronics
I sent an e-mail to Subaru asking if I could use my iPad as the iPod and iPad cables are the same. They said - "Thank you for taking the time to contact us and for your interest in Subaru products.
The iPad does not function with our iPod interfaces. As for podcasts and audio books, if on an iPod, they do play through our iPod interfaces. If using the iPad, the podcasts and audio books would not play."
Does this seem correct? As the iPod works and the USB port allows other portable drives to work, why wouldn't an iPad work?