Rather than calling it doesn't work. I would say it is not likely to work.

Ret in melee DPS gear can't heal for long. OOM too quick. Burst healing output is decent though. But can't sustain it. Its more like save you once kinda thing. and the healing output is not close to Holy.

Ret in Holy gear can't DPS. The melee dps is too low.

Shockdin is way better (both DPS + healing) right now though I don't see Blizzard will tolerate holy paladin's current status.