Beginning with the forces surrounding the Vampyres located in the Underworld- they were a force that those in the Dark Expanse had managed to squeeze through the eyes of the Celestials in the period of the last 1000 years as they grew themselves in name and power in the Light Expanse.
The Vampyres held a special relationship with a few powerful figures in the Dark Expanse through the powerful being that held the entire race on her shoulder, the Vampyre Progenitor.
With her death being one of the many results coming out from the war more than one thousand years ago, the Vampyres were more than willing to act as spies in enemy territory, becoming a stable force over the past hundred years as they came to prominence in the Underworld.
The Vampyres also fit this task perfectly as they held abilities that allowed for complete secrecy, the covert qualities of their techniques making them move unhindered for the past hundreds of years.