The Pales are demonic planes outside of existence in the "Near Void" in the Shadow World cosmology. While not related to The Unlife per se, they are indirectly, by paralleling the chaotic aspects of our own reality. (The demonic must manifest from dark essence in our world.) The Pales were so named by the Lords of Essaence because "all other realities paled" to their own. Not necessarily evil, Demons of the Pales are so intrinsically alien, they are uncontrollably insane and unpredictable. Thus, they are only used for force by dark mages, and were often related to the Dark Gods in their I.C.E. Age form. There are portals leading to the Pales on Charon (Lornon). The "Outer Void" had no common reference points with our own existence, and only very unusual conditions and the most powerful gates would allow access. The Outer Void is dominated by an extra-planar collective called the Agothu, which are so incomprehensible they would inherently destroy the world in their sheer incompatibility.
Demons "Beyond the Pale" are essentially demi-gods, and cannot be controlled by ordinary means. "Demons of the Essaence", who are more directly related to The Unlife than those of the Pales by virtue of belonging to the same axis of cosmology, are of a fundamentally different nature. The only exception are Ordainers, who occasionally become so chaotic and unruly, they are thrust or banished into the Void. Though "Outer Planes" such as the Black Hel can be tranquil, those merely "beyond the pale" are incomprehensible, in much the same way as The Rift in modern GemStone. Some books treat The Void as a place of The Unlife, and others as something else entirely. The ultimate effect of sundering the world to any of these otherworldly factions would be utter destruction.
While these are the valid definitions within the Shadow World setting, they are categorized differently in the Rolemaster bestiaries, where Demons of the Void are souls of our world who become demonic on other planes of existence. These were re-cast as "Conformer" demons (called "Older Ones") of the Outer Void for Shadow World. Within that scheme the Demons of the Pales are the "natural" denizens of other planes (though still a "hopeless" prison for the wicked), and there is no category corresponding to Demons of the Essaence. There are, however, other categories. One of those classes of "non-demonic" extra-planar entities directly corresponds to most of the creatures in The Broken Lands, though these are not considered extraplanar beings for game mechanics. They would be non-canonical in Shadow World. Since GemStone III was not bound to a given interpretation, pieces were freely taken from potentially inconsistent sources. Of special consideration is the point that in the Rolemaster scheme, the Lords of Essaence were fallen immortal spell-casters, so the former servants of Kadaena would plausibly have become Ordainers who were banished to the Void. Likewise, the "malformed spirits of fallen demigods" would include the category of Ordainers, which is relevant to the relation of the Dark Gods to the "spirit born of death" premise behind The Broken Lands.
Behind the Scenes
While the cosmology of GemStone is not especially well-defined yet in a systematic theoretical sense, DragonRealms is the same world set thousands of years in the future. The "Planar Void" is still a concept in that context, referring to the "absence of existence" that is a wall or barrier between "planes of existence", perhaps the nothingness of voids from implosions. When these planes are allowed to intersect, their energies and physical laws bleed into each other, with the ultimate extreme being total collapse such that they merge as a single universe. These effects are typically regarded as pollution. Elemental planes are described essentially the same way in GemStone. There is also another place called "The Void" in the Spiritual Plane, which is roughly the same thing as Purgatory.
The underground stronghold on the Coastal Cliffs is apparently part of the Etrevion story arc, with the bounders and kappas potentially being the victims of a transformation curse and dark wisplings as weak nether elementals. Bandur Etrevion crushed the heretical sects with "foul creatures of his own creation." The interesting point is that the claw marks in the stone walls and decapitated head in the tree are hallmark behaviors for Demons of the Sixth Pale, which would mean the story is implying that Bandur was in the business of making such extra-planar beings artificially. The pulverized guard would be consistent with Demons of the Fifth Pale as well, which are so strong they effortlessly punch through steel doors and stone walls. While the lower level of the Coastal Cliffs was partly related to the fall of Quellburn, the Black Sands was subject to sorcery with its frozen lava castle, and may even refer to Death's domain and the Dark Desert of Discworld as yet another limbo allusion.