Unless Gaven had completely lost his mind, he wouldn't send Gnolls to face an actual Giant Dragon. Given their current nature, they would surely turn traitor in the heat of battle, turning their weapons on themselves, not just the Eagle Cliff Burrow Gnolls but also those of the Blackwell Tribe are likely to behave in this manner.
Gaven was confident he could reform them, but that's for the future, not now. At present, they still acted on primal instincts.
After all, ask a group of farmers to slay a dragon, and they will decline, too. Their situation wouldn't be any better than that of the Gnolls.
Slaying a dragon is an act that requires both great courage and great wisdom.
