Ah, interesting! I was going off of the in-game spell description for Animate Dead, which is probably the issue. The spell lists the summons as the following:
Levels 1 to 3: Tyrantfog Zombie
Levels 4 to 7: Skeletal Warrior
Level 8+: Skeletal Chieftain
So, by vanilla NWN standards - by the time you qualify for the class and then begin taking Pale Master levels, you'd need to be roughly character level 15 before you could summon the skeletal chieftan.
Alternatively, a pure wizard or sorcerer could summon the skeletal chieftan at level 8.
Since a cleric's caster level is considered doubled when determining the level of undead summoned, they can summon the skeletal chieftan as soon as they get Animate Dead, at level 5.
I'm wondering if we'd consider changing the level at which PM's gain access to the more powerful summons for this ability? Since Undeath is one of the main features of the class, it seems like a pretty hard hit for them to be running 7-10 levels behind other classes in summoning the same creature with this ability.