iBook on iPad: turn pages with voice command
No - without some external hardware that would somehow touch the screen for you, voice input is for Siri / VoiceOver and not general accessibility controls.

You might look to a program like Instapaper where you can scroll the view by tilting the device but iBooks doesn't have any accelerometer based controls or voice controls at present. It's not that it couldn't be added, just that it hasn't.