Gonna throw my 2 cents out here real quick, as a lvl 60 BRD who is currently doing lvl 50 dungeons for the anima weapon, with an ilvl of 154, I try to be really cautious of my aggro. I wait a few seconds, I shoot off less attacks, less AOEs, etc, to try and keep from drawing hate. No matter how cautious I am, though, I almost always draw a target or two from a mob, especially if I have to play a song.

I grabbed DRK and played as lvl 30 for a little while and tanking is not a simple task, but neither is DPSing, and neither is healing (lvl 13 conj, lots of juggling involved). They're all a balancing act, and if the team is working together, whether or not the DPS or Healer draws some hate isn't really an issue, as long as the tank can re-grab it and they aren't doing it on purpose (ie: don't pull extra mobs, let the tank go into a room first, etc). It's only ever a problem if the tank looses ALL of the mob, which almost never happens unless I'm in very low level stuff.