They do actually appear in the ARG Bestiary volume 1, and they have existed since the 3.5 version, but. . .
Essentially, the gar are orcs in the D&D sense. Now, of course nothing is that clear cut in Arcanis, and the gar culture is far more complicated and nuanced than the typical D&D or Warhammer Fantasy versions of the orcs. Appearance-wise, they are generally humanoid with art showing them as having prominent canines and pointed ears like the elorii (there is a very specific in-canon reason for that

). They tend to be tribal in nature, focusing on nature and primal magic, and shun settlement and civilization. Unlike normal orcs, they are not fundamentally violent, but are perfectly willing to defend themselves when threatened. Most races view them as stupid, barbaric, and little better than pests. This has led to empires for thousands of years pushing them off their traditional lands and into marginal areas of the world.