Nazgul At Pelennor

[Voralphion]

I would envisage that some of the Nazgul, other than hunting for the ring bearer, could have been assisting in the fight against Lorien.

The hunt for the ring was the most important thing to Sauron so he would've had the nazgul primarily concerned with that. The battle against Lorien was only a minor thing, and possibly only used to tie up any possible help for Gandor, and so wouldn't have had nazgul leading the attack.