is zerato a good cad can u summon it if santurey is not there

What makes a card good is what you can do with it while it remains on the field. Most players dislike it because it can only be special summoned by Tirbuting 1 The Warrior of Zera from your side of the field. But when The Sanctuatry in the Sky is on the field and you have 1 light monster, you've just turned Zerato in to a reusable Raigeki. Over all it all depends on how well you build a deck around summoning Zerato.

Basically, it's a bad card.

It is very situational lets just say that.