Under the Eye of God — David Gerrold

RULE OF BLOOD
Once they had been humanity's last best hope: a race of genetically engineered killing machines known as the Phaestor and their army of deadly Moktar Dragons. Now, the enemy long vanquished, the Phaestor themselves have become the enemy, seizing control of the galaxy and subjugating all lesser species--including humans--to feed their appetite for terror and blood.

On a small, insignificant planet called Thoska-Roole, a ragtag alliance of humans, androids, and bioforms make a last desperate stand against Phaestor domination. Among their number are two bounty hunters, a mercenary starship captain, and a disgraced reptilian warrior. As the Phaestor begin a new reign of unprecedented terror, these rebels prepare to strike back against their vampire overlords and bring revolution to the stars.