Rapidly-accreting black holes and young, rapidly-rotating magnetars (proto-magnetars) are two possible central engines for gamma-ray bursts (GRBs). The midplane of neutrino-cooled accretion disks and the surface of proto-magnetars are both neutron-rich, with a neutron-to-proton ratio np≫1. If a large neutron fraction is preserved to large radii in relativistic, GRB-producing outflows, several observable consequences may result, including changes to the prompt and afterglow emission from the standard fireball model. We describe the results of detailed magnetohydrodynamic calculations of outflows from both proto-magnetars and hyper-accreting disks which predict the nucleonic content of the material at large radii. We summarize the prospects for neutron-rich GRB outflows from individual central engines, emphasizing a fundamental difference between neutino-heated mass-loading in proto-magnetar and accretion disk winds.