I don't agree.
Special Attacks and Special Qualities
Many creatures have unusual abilities. A monster entry breaks these abilities into special attacks and special qualities. The latter category includes defenses, vulnerabilities, and other special abilities that are not modes of attack. A special ability is either extraordinary (Ex), spell-like (Sp), or supernatural (Su). Additional information (when needed) is provided in the creature’s descriptive text.
When a special ability allows a saving throw, the kind of save and the save DC is noted in the descriptive text. Most saving throws against special abilities have DCs calculated as follows: 10 + 1/2 the attacker’s racial Hit Dice + the relevant ability modifier. The save DC is given in the creature’s description along with the ability on which the DC is based.
The DC for the fear aura is 10 + half the sorcerer's racial hit dice + the sorcerer's Charisma bonus.
His hit points don't change, per the spell... so he has 18 class levels, and no racial hit dice.
With a Cha of, say, 22, then, his Save DC is 10 + 0 + 6, or 16.
If he were an 11th level Rakshasa sorcerer (whose 7 levels of sorcerer spellcasting ability stack with his class levels), then when he Shapechanges, his Save DC would be 10 + 3 (half of his 7 racial hit dice) + Cha modifier. (Of course, that's an ECL 25 character.)
-Hyp.