Healers DPS is needed for every content, cause more DPS = quickest kills/dps check. It's not a matter of being necessary/mandatory or not, you're just a bad healer if you're not DPSing. It's like having two hands but using just one of them all the time.
It's almost the same thing for DPS when it comes to stuff such Second Wind, Rend Mind, Dragon Kick ect., with the only difference than healers DPS does affect progression a lot.