As Russel Norman makes clear in that interview, the Greens' position is set by their membership, which reconfirmed their 2011 position. You can read it here. And to save myself the effort of writing another post, I'm simply going to quote what I said about it last time:
Being a party of policy rather than tribalism, they're not willing to rule [support for National] out entirely. But being a party of policy, any assessment is going to be based on the merits, and the degree of compatibility between National and Green positions. And any honest assessment would show that the two parties are deeply incompatible.
The Greens support clean rivers. National wants farmers to dirty them for greater profits. The Greens want action on climate change. National is still a party of deniers, who wants to subsidise polluters. The Greens want an end to offshore drilling. National's plans for economic growth are predicated on it. The Greens want to reduce inequality. National wants to increase it. Unless National changes its position on most of these issues, then there is no hope of the Greens putting National into government. And if people think that the Green leadership will be seduced by the baubles of office, remember that its the wider membership who will have the final say on any arrangement. I think its "highly unlikely" that they would support any arrangement which saw the Greens providing confidence and supply to the current National Party. But if they do, well, they'll get what they vote for. Coalition with a friendly party with a high degree of policy compatibility is fraught enough. Coalition with a party fundamentally opposed to your values seems to be a slow and unpleasant form of suicide.
The other point I'd make is that being a party based on policy means always being open to the possibility of cooperation, even if you recognise that in practice, its never going to happen.
What is interesting in that interview is Norman's wriggling over the question of their relationship with Labour. Espiner (in horse-race mode as usual) interprets this in terms of coalition preferences, and so misses the real picture. In the long term, the Greens want to throw off their "junior partner" status and be recognised as the leading party on the left (rather than just being it in practice). This means eating Labour's vote and supplanting them as the largest party. Labour's failure to gain any traction during this campaign is an opportunity to advance that project, and present themselves as an effective, growing, principled party in contrast to a bunch of stagnant tired has-beens. That's pretty obvious, but there's a world of difference between recognising it, and telling Labour MPs openly on the radio "we're coming for your jobs".