Hexagonal boron nitride (hBN) is one of the most suitable 2D materials for supporting graphene in electronic devices, and it plays a fundamental role in screening out the effect of charge impurities in graphene in contrast to inhomogeneous supports such as silicon dioxide (SiO2). Although many interesting surface science techniques such as scanning tunneling microscopy (STM) revealed dielectric screening by hBN and emergent physical phenomena were observed, STM is only appropriate for graphene electronics. In this paper, we demonstrate the dielectric screening by hBN in graphene integrated on a silicon photonic waveguide from the perspective of a near-field scanning optical microscopy (NSOM) and Raman spectroscopy. We found shifts in the Raman spectra and about three times lower slope decrease in the measured electric near-field amplitude for graphene on hBN relative to that for graphene on SiO2. Based on finite-difference time-domain simulations, we confirm lower electric field slope and scattering rate in graphene on hBN, which implies dielectric screening, in agreement with the NSOM signal. Graphene on hBN integrated on silicon photonics can pave the way for high-performance hybrid graphene photonics.