There's nothing like that in the NDA. Why jump to these false conclusions about a document you have not even seen?
Because it is implicit - it is not Hyperion not allowing anything, it is AROS that cannot risk having AmigaOS developers contributing, because who know what Hyperion might do then - exactly because the documents that you refer to are not public.
I must say that I've lost count of the number of times that a current or former Amiga OS delevoper has bemoaned the fact that they cannot contribute to AROS because of the NDA they signed with Hyperion. Let's also not forget the huge number of developers who opened up to the public that they wanted to work on Amiga OS but had to make the hard choice not to because the NDA presented to them was just too restrictive for their liking.
