Diamond offers 2 tribes, the Chimbu and the Daribi, as examples of differing receptivities to innovation:
Do you think he would accept larger, continent-wide differences in receptivity and how problematic might cultural factors prove for Diamond's arguments?
Any answer to this question is pure speculation, but I think that Diamond would only accept the idea of larger, continent-wide differences if there were only a very few distinct societies on that particular continent. Otherwise, he would argue that there are too many societies and that they are too different to generalize about.
As for cultural arguments in general, as long as the cultures differ in random ways across continents, it is not a problem. Diamond does not say that cultures don't differ -- he just says that one continent won't have cultures that are all similar and that all differ from those on another continent.
If we were to find, though, that all (or the great majority of) African societies were different in a relevant way to all (or a great majority of) European societies, then there would be real problems for Diamond's theories.