Hi
There is no built-in support for e.g. .blend, but custom data providers are supported via HairAssetCustomData, which can be plugged into a HairAsset (select type ‘Custom’). The provided curve data will then pass through the existing HairAsset processing pipeline for formatting/validation and clustering.
Yes, this is fine. Alembic data (and other external curve data) is used only as source material for when building the runtime ready curve data that is stored in a HairAsset. The original source material is never accessed by the runtime.