Of all of the existing ones, Osteomancy is the one that's utilized the least in the flavor text of Arhosa. Rituals, Runes, Necromantic, Spellsong, Threshold, and Fleshgrafting are all intimately tied to given deities in both flavor and mechanics. Indeed, the central conflict of the setting is Rituals against Necromantic.
Thematically, Osteomancy is supposed to the magic of the village shaman, wary of outsiders and conducted via rituals and fetishes. So there's certainly room for it in Arhosa as a less cruel way to access Drancedigaeth's (Death) gifts - especially as Ritual magic alone doesn't necessarily give the Death god the scope of worship he needs for his conflict with Lledrith (Magic, Undeath). Whether the mechanics are there to give the thematic needs backing is a relevant question.
The short answer is that it fits into Arhosa, but I haven't done the work necessary to really smooth over all the rough edges of the setting flavor, and it's the system that suffers the most.