Based on their size, physical characteristics, habitat, and likely activity levels, I'd say the Au Ra are almost certainly endothermic (warm blooded). Ectotherm (cold blooded) animals tend to have restricted habitat ranges and activity levels based on local weather and temperatures since they depend on external heat sources. The naming guide specifically names a tribe, the Kagon, that are purely nocturnal. An active nocturnal nomadic lifestyle would be impossible for ectotherms.
On dragons, you could draw parallels with dinosaurs (another strain of extremely large reptile-like animals). There is currently some debate over whether dinosaurs were true endotherms (like their descendants the birds) or were mesotherms (a compromise between endo and ectothermy).