We show theoretically that polariton pairs with a high degree of polarization entanglement can be produced through parametric scattering. We demonstrate that entanglement can emerge in coincidence experiments, even at low excitation densities where the dynamics is dominated by incoherent photoluminescence. Our analysis is based on a microscopic quantum statistical approach that treats coherent and incoherent processes on an equal footing, thus allowing for a quantitative assessment of the amount of entanglement under realistic experimental conditions. This result puts forward the robustness of pair correlations in solid-state devices, even when noise dominates one-body properties. In particular, we propose an operational method to measure the entanglement of formation, out of a dominant time-dependent noise background, without any need for post-processing. Our study provides a suggestive perspective towards hybrid all-optical quantum devices where quantum information can be efficiently generated and controlled within the same structure.