Can I use a Vittoria Zaffiro 700 * 25c road bike tyre with a hole in outer rim of the tyre? My road bike tyre got punctured couple of days ago and I just noticed that it resulted in a hole in the outer wall of my tyre. How can I close this hole? I rode just 500kms on this tyre so I am not sure if I need to replace it with a new one
Install the tire and pump up to pressure and see if there is any bulging which would indicate the chords are damaged. Damaged tires belong in the trash.

If there is no sign of chord damage and you decide to use the tire, I would strongly suggest 2 or 3 layers of duct tape or similar as a patch on the inside.  Not only will this provide additional strength but it will reduce the chance of gravel or debris getting into the hole. 

FWIW, for small holes such as this I will use Shoe Goo to fill the hole and prevent debris from getting to the tube.  First I inflate the tire to a pressure above where I ride and then work some Shoe Goo into the hole. After the Goo cures overnight and the tire pressure is reduced to normal, the tire will squeeze the hardened Goo and hold it better.  If unfamiliar with Shoe Goo, it was originally marketed for repairing worn tennis shoes. It goes on like silicon caulk, remains flexible but is much harder than caulk. 

Last tip: The repaired tire is always installed on the back wheel and I position the repair at the valve stem so I can easily check for any signs of bulging every time I inflate the tire. 

Shoe Goo