Originally Posted by
Ngugi
They had not only been rare after the Battle of the Five Armies in 2941 Third Age, since between ca year 1000 Third Age to the year 3019 Third Age the only Black Númenórean ever seen was The Mouth of Sauron himself, so while fragements of that people yet existed somewhere in the unknown far east and/or unknown far south they did not show up except in an individual case.
By "undead" I presume you mean the three of the Nazgûl who were of Númenórean origin? Because no others existed (strictly speaking it may be questioned if Black Numenoreans even existed when the Ringwraiths came about, and on top of that we do not know if the three Númenóreans who got rings were wicked).
That said, if to add BNs to a late Third Age-game then proposed solution is the clearly most proper solution.