The British Navy during Nelson's time was composed of not only British sailors, but many other nationalities. The crews of the ships that fought at Trafalgar included sailors from America, Ireland, Prussia, Sweden, the West Indies, Africa, and even France and Spain against whom the British were fighting. On Nelson's ship HMS Victory there were 22 nationalities involved in fighting on the British side
I recently read a book called Trafalgar by Roy Adkins.
It says 90% of the Victory's crew were from the British isles. Of the remainder, about a third were from North America. There were also some from the West Indies, ethnicity not given. The reminder, say about 6% of the crew, were from elsewhere.
I'm not saying that people born outside the UK didn't make an important contribution to the British war effort. They absolutely did, and two WW2 examples would be the Maori Battalion in Italy, and the Indian Army in the Burma Campaign.
But NZers, South Africans, Americans (at least in Nelson's time) weren't 'ethnic' or 'foreign' in the usual meaning of those words. They were white, English-speaking, generally with UK-born parents or grandparents, some probably born in the UK too, and if asked, most would have said they were British or Irish.
NZ passports had "British subject" marked on them until the late 70s.