The integration of wave energy devices and coastal structures may be an innovative and sustainable way to achieve energy production purposes with a secondary benefit of coastal protection, which can increase accessibility and reduce the costs of wave energy technology. In this paper, a 3-D theoretical model was developed to investigate the hydrodynamic efficiency and breakwater function of a periodic array of oscillating buoys embedded in a caisson breakwater. The generalized radiation problem was solved to derive generalized radiation force. The theoretical model was validated using Haskind's relation and energy flux conservation law. The influences of wave/geometrical parameters and PTO damping were revealed. In particular, hydrodynamic phenomenon of multiple orders reflected and transmitted propagating waves and their influence on wave power extraction and coastal protection was examined. Results show that a satisfactory hydrodynamic efficiency and coastal defense are realized simultaneously under oblique waves for this proposed system. A decline of hydrodynamic efficiency is found beyond a critical wavenumber, accompanied by the occurrence of the strong reflection phenomenon. The findings of this paper contribute towards the preliminary design of the hybrid breakwater-WEC system for the synergy effect between the wave energy devices and breakwaters.