Two-stage hybrid analog/digital systems have been proposed in mmWave scenarios with the aim of decoupling the system gain (boosted by the number of antennas) from the number of radio-frequency chains. In light licensed or unlicensed bandwidths of the electromagnetic spectrum, enforcing limits on the radiated power levels of the radio nodes can be instrumental in guaranteeing coexistence of uncoordinated communications. Inspired by this rationale, we propose an efficient two-stage precoding design strategy that aims at maximizing the overall system spectral efficiency while guaranteeing specific constraints on both the total transmit power and the output emission levels. Capitalizing on the sparse nature of the mmWave channel, the analog precoder is built by selecting steering vectors that are tailored to the radio propagation environment, while side-lobe level control and multi-user interference management is entrusted to the digital precoding scheme. The proposed algorithm is shown to deliver the same performance as the equivalent full-digital scheme in case of light-to-moderate constraints on the radiated antenna pattern and practical quantization levels at the phase shifters composing the analog module. Numerical analysis underlines the inherent trade-off between coexistence guarantees (in terms of constraints on emission levels) and system performance, and suggests that an ad-hoc precoding design should be paired with properly devised medium access control and resource management mechanisms for handling uncoordinated system deployments at the highest efficiency.