[Tuor of Gondolin]

There seem to be two interpretations here of
"yet it was but one and not the greatest of the hosts that Mordor now sent forth"

a---That there were larger armies sent elsewhere or kept in Mordor
b---That the army of the Witch King joined with a larger army (presumably coming from the Black Gate).

I've always read it to be option "b" above, given presumed logistical limitations of sending forces from Minas Morgul, though I suppose it's open to interpretation.

As for dwarves not involved in fighting in the war of the Ring, they were crucially so in Erebor.