There's actually a weak-point in using that spell.
The creature’s combat statistics are those of a 2 HD humanoid skeleton, except that it also has a wight’s energy drain supernatural ability (see the Skeleton and Wight entries in the Monster Manual for details).
Energy Drain (Su)
Living creatures hit by a wight’s slam attack gain one negative level. The DC is 14 for the Fortitude save to remove a negative level. The save DC is Charisma-based. For each such negative level bestowed, the wight gains 5 temporary hit points.
Abilities
A skeleton’s Dexterity increases by +2, it has no Constitution or Intelligence score, its Wisdom changes to 10, and its Charisma changes to 1.
(Su) abilities have their DC set to 10 +1/2 HD +ability mod.
A 2-HD undead with a charisma of 1 means the Fort DC to remove the negative levels is only 6.
Even if a 10th level fighter were taking a -9 penalty to the Fort save from having 9 levels drained, he's still likely to pass the save on a 4 or better on the die. (Base +7, +3 Con, +1 magic).
Still, there's no save to remove it until the next day, and unlike a wight, the skeleton can attack twice per round. So, still a decent spell in combat, though there isn't really any good way to boost its abilities (as it is basically a construct). Or does it actually count as undead? I doubt it.
So, it's not perfect for my purposes, but it will suffice if there are no other options that come to light.
(I want to take a former player's character hostage and use it as leverage with the party, then take him out of the picture, so far as adventuring with the party as a DMPC, by level draining him to a point where it would be suicide for him to join the party after he is freed.)
Of course, the entire point of that would be made moot by the party casting Sending, contacting a Hathran, and asking her to cast greater restoration on him...
Darn me having the PC's save the world...