We use WHMs, RDMs and SCHs in our CP parties for main healers and I even have a RDM mule on standby in case we can't get one. A main healer is necessary in TP style CP parties because the melee's are taking a lot of damage but the CP gain is far superior to BLMs blowing up crabs. At 1000CP in I was hitting 65K per kill at chain 13 in our location, and chains lasted until 38~40 when it would reset back to 28~30K per kill.
The biggest piece of advice I can give to people trying to get CP, be creative.
