Racial abiltiies are weird and difficult to easily quantify. Terror Hound’s Eye of the Thylacine stacks multiplicatively, not addtively, so instead of 15% dodge chance + 15% dodge chance = 30%, you get ~28%. Horror Hound’s bleed chance doesn’t stack at all, but doesn’t say so, in comparison to the Hell Hound’s 200% damage bonus that explicitly states it won’t stack.
Diabolic Horde abilities do stack, but there’s no text to indicate a yes or no on the topic, probably due to a lack of room in the description box.
There’s also Gust Aura and Lash of Undeath, which I know stack multiplicatively, but I’ve never seen Abnegation or Lifebinder stack on themselves either multiplicatively or additively.
The short answer: I don’t know everything.