My apologies if this sounds like an argument from authority, but anyone qualified to speak about these theories thinks they are untrue. The problem is that there is simply no evidence backing the theories up.

Michael King has to the the following about them (Penguin History of New Zealand, p.29) "The problems with these theories is that there is no evidence for the claims. Despite a plethora of amateur theories about Melanesian, South American, Egyptian, Phoenician and Celtic colonisation of New Zealand, there is not a shred of evidence that the first human settlers were anything other than Polynesian"

Victoria University Professor of New Zealand studies Richard Hill has said that "Not one of them has ever passed any remote academic scrutiny"

University of Auckland associate professor Hugh Laracy has said that "[The theory] has been around for a while but it's been thoroughly disposed of by academic specialists."

A more detailed take down of there theory can be found here:

http://books.scoop.co.nz/2008/11/18/no-to-nazi-pseudo-history-an-open-letter/

References

http://www.stuff.co.nz/national/8123896/Stoush-over-pre-Maori-colonisers-theory

http://www.nzherald.co.nz/nz/news/article.cfm?c_id=1&objectid=10856261