I have always been a DPS healer (WHM). The last thing I'm going to do during a dungeon (mega-pull) is regen before the tank has settled. Not only does that send hate my way (which in turn draws my attention away from contributing damage) but typically slows the tank down. There is literally no reason why regen should be thrown early in that circumstance given the tank will be running (taking less hits as enemies chase), everyone is on the move (thus stray mobs causes problems), and there's literally no benefit other than the tank shrugging off a few auto-attacks, to which I would say that if they needed regen to do that than they shouldn't be mass-pulling anyway.

I let the tank round everything up and then unload QC-Holy, AIII then rotate between heals and damage. This is obviously a lot different than pre-HoT'ing tank(s) before boss/single-target pulls -- regen to your heart's content in that case.

As someone with a max PLD & WAR, I have encountered many Healers of the AFK and/or 'regen spam' variety. What's funny about AFK healers is that despite them standing around staring at healthbars, they're typically no faster at healing during critical moments than a good DPS healer. As for the regen spammers, yes, I'll click-off regen continuously if they're doing so pre-pull. Thankfully, the majority of this type of Healer tend to be a sprouts, some of which will listen if you ask them to stop doing it. I have yet to encounter someone who didn't get the message, though if/when I do, you can be certain I'll resort to single-target enmity strats so that the Healers gets a lot of aggro-love. They can learn the hard way or kick me so I can insta-join a new run with a different Healer.