The gnoll camp that turns into an undead gnoll camp at night do not seem to respawn if cleared. It will repop if the time changes from day to night or vice versa, with the new mob types for the time, but normal repops do not seem to happen.
Also, when the undead are out, skeletons in the camp seem to be encumbered - they will agro, but they do not seem to be able to move. The other undead inhabitants seem fine though.