Disoriented enemies have a chance to wander a little, they probably won't attack during that time, their spells are interrupted-- but any damage snaps them back. Disorient is gimped stun.
That doesn't make the bombs unuseful by any means-- that disorient effect is invaluable at times. But you need to know the score before you start flinging them around.
Yep. My engineer isn't very high level, but I confirmed this in a duel. I threw a grenade and it was several seconds before he fully recovered (other players don't have the AI's instant reflexes).