I don't know 100%, but the iPad 2 is thinner than the iPad 1 so it will be a loose fit. And the iPad 2 also has a front facing camera and the rear camera. And that Defender for the iPad 1 won't have the cut outs for the cameras.
However, it has been reported on Macgasm that the iPad2 Otterbox Defender will be out on Friday ($89.95) -- Otterbox about to debut Defender for iPad 2 | Macgasm. There's also a vendor on Amazon selling the same for 15% less ($76) -- Amazon.