I can't recall any recent Oda 1580 campaign that I've played where they weren't allied. I've always had to face them both in Mino within the first year.......and every year thereafter until I kill one of them off

AFAIK, the appearance of the Dutch has no relationship to the Portuguese showing up. I could be wrong, tho'.....

I never wait for the Dutch anyways. I take the first Portuguese offer and run with it until I have a gun factory and muskets.