Family knowledge, including oral history, are valid sources. I would include the information along with a description of where the information came from (although not specifically naming living people, for privacy reasons).
With an accurate description of the source, other readers can judge for themselves how much faith to put in the information.
If you have a whakapapa diagram, uploading a copy of that (obscuring details of living people for privacy) would be a good idea.
A little tip for looking up records in the NZ BDM index, you can put a single dot "." in the Surname field to search for any surname -- helps with finding records that may have been misspelt. Although as you will have found, many Māori births were not registered with the government.