You do know that doing that would injure him more? If you have a neckbrace on and no helmet you are 10 times more prone to breaking your neck. Thats why if you ever stop to look at the track and you take your helmet off, you should unclip your neck brace aswell so your head can roll normally.
Im not. It would be nice to see pro's like him wearing helmets though. They are there to save lives and DH is not a forgive full sport if you crash (trust me i learnt that the hard way!)