Yak does.
Sometimes the Sheng group gets a runaway from the doors that needs to be taken out, and certainly the door group teams benefit from the cape. Imp has plants and flowers that can die in time to benefit when the Imp ports to your side - and anything to speed that fight up is appreciated. I kind of doubt that the Emperor's Illusions proc the cape buff as I can never get my bear green to fire but maybe the cape works.
I suppose Lu Zhi's and Keiara's charmed raid members that get killed rather than saved will give the cape buff, too.
But I agree, the cape's buff won't be used in most boss fights.