We perform united atom molecular dynamics (MD) simulations to quantify the role of flow-induced nematic order in polyethylene (PE) crystal nucleation. Blends of periodic stretched and nonperiodic unstretched chains are used to mimic realistic PE samples in which only a fraction of polymers are stretched by flow. We show that, when the fraction of stretched chains and their degree of stretch are varied separately, the nucleation rate collapses onto a single curve when plotted against the imposed average nematic order of the monomers but fails to collapse when plotted against the average chain stretch ratio. For shallow quenches and a low imposed nematic order, the nucleation rate is low but increases rapidly with increasing the imposed nematic order because of accelerated formation of the nematic precursors with a high enough uniaxial order for crystals to nucleate rapidly inside them. A second regime occurs when the imposed order is sufficiently high or the temperature is low enough that the nematic precursors form instantaneously, and further increases of the imposed order affect the nucleation rate less strongly than in the first regime. Our findings should spur the development of quantitative theories for flow-induced polymer crystallization.