Yes, you can activate the camera without activating the LED. The LED is not directly wired to the power supply.[0]
[0]http://www.washingtonpost.com/blogs/the-switch/wp/2013/12/18...
Edit in Reply: Not necessarily. It's probably still possible on modern Apple hardware, albeit with a lot of firmware hacking, according to the authors of the paper: http://apple.stackexchange.com/questions/117937/how-to-use-i...