My gut instinct would be 'no'. But there is always the possibility (at least in the UK/Europe) that your friend could argue he is being discriminated against under the Human Rights Act and Discrimination From Disabilities Act.
My reason for my gut instinct being no is that even if the airline introduced a total 'no nuts' policy in their on-board food and snacks, it would be extremely difficult to enforce what every passenger brings on with them.
I don't think the allergy itself would prevent him from getting the required medical certifying him for flight, more it would be the airlines concern with his allergy on board.
Do keep us updated on this, I would be curious to know the outcome.