I would suspect that in most Japanese-foreign marriages, the foreign parent is the father/husband.
It's an interesting subject.
If I remember correctly (and it's been a while since I looked at the actual numbers versus anecdotal sources, so I could be off on some of this), it's true that for most Japanese-western marriages, the foreign parent is the husband.
However, with marriages to Asians, the numbers reverse, and the foreign parent is more likely the wife.