i have used a bunyip at dust devils and at armoured zombies. i know that zombs are single cb but dusties arnt. and i know familiers can attack dusties cause back when i had my terrorbird it would help me in killing dusties.
in the summoning guide it says that bunyips fight. but i use mine and i have never seen it do one attack. it says bunyip fights training att and im training str and my att hasnt moved at all. so i think you got some wrong info