Can i use deck blocks with fence if i bury them in stead of cement?

You can, but you shouldn't. When you use cement, the liquid cement forms to the imperfections of the hole you pour it in, which is what helps hold that fence post in place when there are high winds, or the inevitable kid trying to use the fence for climbing practice. If that fence falls over when someone is trying to climb it (even if it's a kid or a burglar), you can and will be held liable for installing a fence without proper code requirements. It's just not worth the risk.