Rogue hide/sneak-how it affects aggro in zone

[nwin]

I know if I go in a zone and I'm far enough away from a mob KOS to me, and hide/sneak, I can run up to him all day and he'll never see me.

How does this work in a group setting? Say I'm grouped, and my puller engages with a mob, dies to it. Would I gain any aggro? I would think not, unless I was within aggro radius or engaged the mob, correct?

The other part are trains.

If I'm at zone entrance and someone runs a train there, so long as I hit hide prior to mobs getting within aggro radius, I should be good, correct?

Also, can anything see through hide/sneak?