We investigate the spectral coexistence feasibility of analog optically driven mmWave antenna beamforming over dispersive fiber links within standardized dense wavelength-division multiplexing (DWDM) grids, targeting next-generation wireless mobile network broadband use cases. Our analysis focuses on integration with legacy passive optical network (PON) infrastructure, using three representative deployment scenarios to evaluate compatibility under practical spectral constraints. We present a use case-driven spectral feasibility assessment of analog radio-over-fiber (ARoF)-based mmWave beam steering over DWDM grids, using a numerical framework that evaluates beamwidth requirements under link distance, carrier frequency, as well as fiber and component spectral constraints. We demonstrate that ARoF carrier frequency optimization, governed by WDM grid and component spectral tolerances, enables optimized beam steering resolution.