is strider recruiting zombies

[Shadow of Udûn]

would that imply the armies against Sauron were stronger and braver of heart than his forces

I don't think so. Only the bravest of the goodies (gandalf, aragorn, Eowyn) actually fight against the Ringwraiths, and they have knowledge as a weapon i.e, they know that the ringwraiths can be overcome, or like the hobbits at weathertop, they have no choice. Look at the reaction of the ordinary soldiers of Gondor and Rohan at Minas Tirith - they flee from the Nazgul. I don't think it means that the Corsairs are less brave, they just don't know what they are fighting.
BTW, in norse mythology, ghosts can harm people (read the Saga of Grettir the Strong). Besides, I always thought of them as being more like skeletons animated by the spirits - that could still harm and be harmed, though it would take a lot to stop one i.e, crushing their bones completely, and obviously killing them would be impossible (coz they're dead).