Synchronizer cells are basically synchronizers which are to be used in your design instead of you writing the code for a synchronizer. These flip flops are usually designed with specialized flip flops and precalculated routing and placement.
I don't know what does the reset have to do with this.
It is not about synthesis process. It is about designing a reliable synchronizer whose probability of failing reduces considerably compared to a generic synchronizer. Not all companies have such cells. Find out if yours does and find out the feasibility of using them.