I think it's very unlikely that their nose design is illegal. It affects the design concept of the car as a whole so they would have made absolutely sure that it's legal, and the regulation itself seems fairly simple.
If anything I would argue that McLaren's design is more in the spirit of the rules, which are there to improve safety by lowering the noses. The other teams have their noses as high as possible and McLaren don't, so by this interpretation the McLaren nose is safer?
If anything I would argue that McLaren's design is more in the spirit of the rules, which are there to improve safety by lowering the noses. The other teams have their noses as high as possible and McLaren don't, so by this interpretation the McLaren nose is safer?