I have never felt it was a great idea to attach a camera to a bicycle helmet. I have had concerns something that large on your helmet would alter the effectiveness the helmet was designed to provide. The camera and mounting bracket could deflect the movement of the helmet upon impact or weaken its crash protection properties. I'm not aware of any manufacturer testing to prove the point.
However, Howie Johnson of the Sumpter Landing Bicycle Club wrote an article on this topic in a recent edition of their newsletter. He described the 2013 incident involving Formula 1 driver Michael Schumacher who suffered a serious brain injury in a skiing crash while wearing a camera affixed to his helmet. Testing was performed after the crash by ENSA (world-renowned ski and climbing academy in France) to look at the effect of a solid object between the helmet colliding with a rock. The results were the helmet was destroyed even when the camera was undamaged. Not a good omen.
Without any other serious data to rely on I would always lean to the side of caution and not attach one. The risk seems way out of proportion to the reward of the images you want. There are other ways to get most of the same images. There is a reason some manufacturers design helmets to prevent attachments.
You may consider this option which Kati located from Giro:
Montaro MIPS helmet by Giro ($150) which includes built-in camera mount with breakaway interface; Universal helmet mount for all other Giro helmets (Accessory Mount Camera and Lights).