XWARREN,
I see mummy as an option in the Spell Compendium for SU V. I am concerned with the strength of the summons for Create Undead you list. The third and fourth ones are not an improvement even though they are when the PC is higher level.
Also, Spectres are much weaker in NWN then in PNP. NWN has many undead and level drain immune baddies. A spectre can't even inflict physical damage (as they are incorprial). This means that there are lots of fights where the spectre is of no use to summon. So the highest summons for create undead has little value even if you made the spectre a higher CR version.
P.S. Even the Summon Undead IV Wyvern is better then Create Undead at all levels (in my opinion).
EDIT: The fear aura of the mummy can fear golems. Seems odd to me.