I dont have Ninja at 50, but looking at the skill description, the party-wide 10% damage up for 10 seconds skill (Trick Attack) can only be executed under the effects of Hide.
And you can't reapply hide while engaged in combat... It's an opener attack that lasts 10 seconds... and that's it.
Maybe you can reapply it on phase changes when the boss goes away (Shiva after adds, Leviathan diving, Twintania going away while you deal with snakes, ....) and that's it.

So... most of the opinions on this topic seem like bullshit.