It's not specifically stated in the SRD that a character 'in the jaws of a dragon' cannot make a Reflex, but the following is stated under Special Abilities, Evasion and Improved Evasion:
"As with a Reflex save for any creature, a character must have room to move in order to evade. A bound character or one squeezing through an area cannot use evasion.
As with a Reflex save for any creature, evasion is a reflexive ability. The character need not know that the attack is coming to use evasion."
Seems to me the above qualifies as being in the jaws of a dragon. YMMV