Healer DPS by itself is not really engaging. There are no specific rotations or DMG+ buffs given for doing it. What makes DPSing as a healer engaging, is weaving it in between heals. I'd put two months pay that every hardcore healer here is LOVING it when they do this in content. Is it a AoE Balance followed by x4 light speed+gravity then helios? Is it shadow flare + bane inflicted on 10 mobs plus a indom after a big attack? Is it x8 Holy with no MP drained from the WHM and a Bene bringing the tank back to full health on a massive pull?
Healers are ridiculously powerful in this game, and when played optimally, which includes maximum DPS uptime plus timely heals and shields pretty much makes a party invincible. Nothing save a one shot or a tank tossing their keyboard/controller in the air can kill a skilled and experienced healer.