The structural properties and lattice dynamics of Ga1-xMnxN were studied for Mn concentrations from 0.0% to 1.5%. Ga1-xMnxN layers were fabricated by either Mn incorporation during the metal-organic chemical vapor deposition (MOCVD) growth process or by postgrowth ion implantation into MOCVD-grown GaN epilayers. The crystalline integrity and the absence of major second phase contributions were confirmed by high-resolution x-ray diffraction analysis. Raman spectroscopy showed that increased Mn incorporation in the epilayers significantly affected long-range lattice ordering, revealing a disorder-induced mode at 300 cm-1 and a local vibrational mode at 669 cm-1. The low intensities of both modes were shown to scale with Mn concentration. These observations support the formation of nitrogen vacancies, even under optimized MOCVD growth conditions. The slight excess of metal components in the growth process compared to undoped GaN growth and the incorporation of Mn deep acceptor levels favors the formation of nitrogen vacancies relative to undoped GaN. Such vacancies form shallow donor complexes and thus contribute to self-compensation. Electronic defects such as these may be detrimental to the ferromagnetic ordering process.