A New Beginning
There are Ghouls in Dante's Freezer. They are seen fighting the apes, who have invaded their territory.
The Eternal Night
Dawn of the Dragon
In Dawn of the Dragon, the Cheetah hermit in the Valley of Avalar says that the ghouls that attacked Spyro and Cynder are the apes. According to him, they only served Malefor because they were greedy and wanted his power, and they showed no loyalty. For those resons, Malefor turned them into ghouls. They appear as skeletons. (needs more elaboration)