Imperial Guard
Given the limited view we have of the Myth world, it is unknown if Orcans actually existed or not. If they did, they would most likely be beyond the Untamed Lands. Numerous plugins make use of these creatures, most notably The Seventh God plugin. Bungie never stated whether these creatures existed in Myth or not, but if they did, they most likely were from beyond the Untamed Lands.
The Imperial Guard were the elite units that could run and attack with good hard hitting speed. The Orcans and Goblins were a similar race and should both be considered Orcans over all. Though debated, their canon to the Myth world seems more assured than ever given Bungie decline to continue the franchise and the use of many different races have already been established in the world of Myth.
It is unknown if these creatures were active during the war against Alric and Soulblighter, but if so, they would have been staunch allies of the Fallen Lord Soulblighter!