While the Hulu Plus application natively supports landscape mode playback, the Nexus 7 device disables rotation by default.
To enable rotation on your device, and thus allow playback in landscape, pull down on the notification menu from the top of the screen. Tap the “counter-clockwise arrows” icon as shown in the image. This will unlock portrait mode and enable rotation.
You should now be able to rotate your device and watch video in full screen, landscape mode.