The Ominous Orse supposedly make their home in the Gladsome Antglade, but are not "from there" and are thus unaffected by the Imperial embargo restricting travel to & from that region. Early in the story, Adler assumes they live in the lowfolk world, since they speak an archaic form of the common tongue favored by lowfolk, but this turns out to be incorrect.
The Ominous Orse specialize in espionage, and will spy for anyone who can pay their rates. They spy for multiple clients simultaneously, and are seemingly not bothered by conflicts of interest. Early in the Ballad, Marshal Roland uses the Ominous Orse as informants - but later, under Marshal Theronmyathus' leadership, they are vilified by Imperial authorities as being untrustworthy (a not unfair assessment.)
This later generation of Ominous Orse have blood ties to the House of Irenaeus due to Adler's act of venery with an Ixie (while transmogrified into Ixie form) just before his 20-year sojourn in the lowfolk world. Their loyalty to their Sire may supersede their loyalty to their clients .. but then again, who can tell with Ixies?