Heort’s people are Heortlings, so it does seem likely these are Ustrand’s people. Of course, what Heortlings call others can be anything at all — “Horse Spawn” was Greg's term (used for the Grazers in the early days of resettlement).
IMO Vuranostum is a corruption of Vuranoste — note all the Grazer names like Hendroste, Jardanroste, etc. And note that the Dara Happan script has a glyph for -um.