Is the new duel deck Zendikar vs Eldrazi considered standard before the Battle for Zendikar comes out? I have been playing it for a few days and I don't want to waste money buy more of those cards if I cannot play them in standard.
No, those cards are not all in Standard. Some already are, some aren't yet, some won't be.
Some already are Standard: Read the Bones and others have been printed in Standard sets. You can use those.
The cards we know will be in Battle for Zendikar aren't standard yet. They will be after that set actually comes out and enters Standard rotation. Dominator Drone and others aren't available in Standard yet.
Some are old cards that might not become Standard at all. Like other duel decks, Zendikar vs Eldrazi contains many cards from past sets no longer in Standard. Butcher of Malakir and Corpsehatch have not been seen in Standard since the original Zendikar block several years ago. There's no guarantee these cards will become Standard at all.
If you're expecting to buy exclusively cards usable in Standard, Duel Decks are not the product for you. Buy those to actually duel with, or if you play a more open format like Modern or Commander.