Ephere has added Nanite conversion in Ornatrix for Unreal Engine. In this short video I show how to enable it and convert native hair to Nanite.
https://dev.epicgames.com/community/learning/tutorials/Rn1K/unreal-engine-ornatrix-ue-5-convert-to-nanite-and-300-mln-hairs-in-viewport-60-fps