Usually the addition of inorganic particles would reinforce the mechanical properties of NR. By adding nano SiO2, the thermal stability and the storage modulus of NR increase. Refer this article for in depth understanding.
Yes, SiO2 is a good filler for reinforcing rubber. In tires, carbon black is used, hence the black colour of tires. But SiO2 also works very well, and white tires can be obtained using it instead of carbon black. But such material is very senstive to photodegradation ...