You could be lucky. the axle nuts might just have been overtigtened a little by the PO. Don't spin the axle too much before you get to open the hub for inspection. You might be damaging your cones and races further by doing so. I cannot see why it would be rusty if the hub is NOS like you said, unless it was in a shop or vasement that got flooded at one time or stored in a damp place for years. Otherwise, the OEM grease in the hub bearing areas should have protected it from rusting.

Chombi
84 Peugeot PSV