So I want to do a zombie survival game. Humans vs. the zombies. Should I use just the nWoD core or allow Hunter: the Vigil? The player characters will be normal people trapped on an island of zombies so it is not like they are 'in the know' Hunters but some hunter the vigil stuff seems appropriate. Suggestions?

Nothing is stopping you from using the core NWoD rules and augmenting with rules, traits, etc. from Hunter the Vigil where it fits. Honestly, this is your game, you're going to be the one running it, so it is best to work out what rules work for you and go with that.