As it stands now.
You get 1+WL blood knights back from a single casting of Invocation of Nehek.
The reason for this is that the rules prevent a model from gaining more than one wound. But in the case of blood knights you only ever heal 1 wound on a model, then you go to the next one and heal the next wound.
The wording of the spell has to change to something like "units with the vampiric rule only get 1 wound back from a single casting of invocation of nehek"
The same problem comes with the hexwrights, since the wording for raising ethereals is the same.
Even Vargheists suffer from this problem, but it's inconsistent. If the vargheist unit has suffered 4 wounds, you can heal 1 wound, brining the damaged vargheist to full wounds, after that you can heal another wound on the "dead" vargheist.
However this does not work if the unit has suffered 5 wounds. Since you are only allowed to heal a single wound on a vampire model, you can not bring the vargheist to full wounds. And because of that you can not raise the dead one back.
It sounds a bit too good. But arguing this is wrong, and that you should not use RAW to raise more than 1 blood knight/hexwright/vargheist. And at the same time arguing that you should use strict RAW on the lore attribute(I still think its RaW that it can heal characters, but some people dont), not allowing it to heal characters. Is imo stupid. Be consistent, pick either RAW or RAI and go with it.
Either you do both as RAW, or you do both as RAI.