We show a strong relationship between CuPt atomic ordering and misfit dislocation glide plane preference during strain relaxation. A miscut substrate creates an asymmetry in the resolved mismatch stress between {111} glide planes, causing a preference for one glide plane that results in a systematic tilt of the epilayer relative to the substrate. However, a small degree of ordering leads to nearly 100% of dislocation glide on planes opposite to the expected planes from the substrate miscut. This result is explained as a consequence of the asymmetry between {111} glide planes of CuPt-ordered material. Lowering the ordering parameter by changing bulk composition results in a change in glide plane distribution and is accomplished through the formation of new dislocations. Control of the glide plane distribution is therefore possible by controlling the ordering parameter on a vicinal substrate. Knowledge and control of this relaxation mechanism is important for the reduction of threading dislocations in lattice-mismatched devices.