Depends on how you move the camera. Middle mouse button works just fine for me. If you disable handles from the NGUI menu, they won't be shown, and they won't steal input. I'm not sure if I added it to 2.6.1e or not, but in the latest version of NGUI I am working with, handles are only visible when the View tool is chosen (Q), and other tools work as they did before 2.5.0.