The only ones of the erc inherits (that werent being inhereted from the erc-default anyway) were

           `(erc-dangerous-host-face ((t (:inherit font-lock-warning-face))))
           `(erc-error-face ((t (:inherit font-lock-warning-face))))
           `(erc-highlight-face ((t (:inherit hover-highlight))))

and of those erc-error-face was the only one I could see in action. I'm not sure how to invoke the other faces.