It depends on whether the WC is a competition between nations, a competition between countries, or a competition between states.
Nation:
A nation doesn't have to be a state or a country. For example: the Nation of Islam can be considered a nation but made up of people who live in various different states over different countries. Those people are also of many different ethnicities. But it is still considered a Nation. Wikipedia describes a nation as:
http://en.wikipedia.org/wiki/Nation said:
A nation is a group of people who share common history, culture, ethnic origin and language, often possessing or seeking its own government.
NZ Maori is definitely a nation; there just isn't a Maori state or a country that is exclusively Maori. The Nation exists largely within the Country of New Zealand and is largely governed by the New Zealand state.
Country:
(
http://en.wikipedia.org/wiki/Country)
A country is simply land: a geographical area. In this case teams like Wales, Scotland and England are all countries, but they aren't states: they belong the the United Kingdom, which doesn't partake in the WC. NZ Maori are not a country, they exist largely within the country of New Zealand. Often a country will be based on a Nation (eg, Czechoslovakia was a state that broke in to two independent countries (Which were also states) that represented the Czech and Solvak nations.
State:
A state is the land which the government has Jurisdiction over. For example, the Soviet Union was a state that consisted of a group of 14 different Nations/Countries (Countries that were based on Nations). The United Kingdom is a State that consists of 4 countries (Again countries that are based on nations) + Overseas Territories. Japan is a state that consists of one country, one nation made up largely of one ethnicity.
The WC is not about state, because GB doesn't play, it plays as England, Scotland Wales etc. If it's about Nations, then yes, the Maori should play, if it is about countries, then no, they shouldn't, it should just be the Kiwis.
Assuming the Maori did play:
The biggest problem it poses is who does a Maori player play for first: Are the best Maori players picked for the Kiwis first, then the NZ Maori pick at the scraps, or do you nominate yourself as a Maori first Kiwi second or vice versa? I think it would get a tad complicated. The other question is: is a League Maori team going to be competitive (especially if all the best Maori are in the Kiwis).
