I was in training in Tokyo when I was told directly by my Japanese friend that I could (not would) never understand Budo properly because I was not Japanese.
Oddly enough, with as much time as I have spent in Japan, I've never run into that. In fact many of the Japanese I meet are embarrassed that I have a better understanding of something they consider fundamental to Japanese culture better than they do.
There is an excellent interview here with a great 20th century budo teacher who points out, quite correctly I think, that modern Japanese are nearly as culturally different from Sengoku and Edo Period Japanese as Westerners. So if cultural purity is required to understand budo, than no living person is qualified. I'm not arguing particular cultural experience is required. I am arguing that particular historical and philosophical knowledge is. That knowledge is available to anyone who puts forward a little effort and thought.