Many papers consider polarization from radio pulsars (for example, https://www.cambridge.org/core/jour...aray-pulsars/8547BD48EAC9A5C9BF8A38346ED506D1). The polarization is very complicated because it tends to be strongly affected by propagation effects, rather than simple source effects. By and large the polarization is elliptical, which implies a combination of both. I would say that answers to your question also relate to whether you are talking about spectrally integrated or spectrally resolved, because some types of polarization shift the frequency of the light in ways that would cancel out if you don't have sufficient spectral resolution.