I think it'll be weird in asking if I can holy to every DRK I see but I can see that not all DRK's will welcome a whm holy.
This is the rotation I usually do.

(regen skills) CS-swiftcast-holy-Aero 3-holy-assize-holy-shroud. If dps is slow I spam holy.This is for more small pulls and when I have all my skills

(regen skills) CS-swiftcast-Aero 3-holy-presence of mind-shroud-holy spam- benediction.

Of course, I treat every run differently but this is basically what I find myself doing most of my roulette's. Unfortunately I haven't found a thread on what other whm do as their aoe rotation but this is what I think works for me.