You can use trick attack with sniper weapons. You do not add trick attack damage to your attack, but the target is still flatfooted, and you can use debilitating tricks.
The operative's debilitating sniper operative exploit allows trick attack to be used with a sniper weapon (though it does no extra damage), but sniper weapons are unwieldy and require taking a move action to aim them.
If you have debilitating sniper, or any other special ability that specifically allows you to use trick attack with a sniper weapon, using trick attack with a sniper rifle counts as taking a move action to aim the weapon to use the range increment listed in the sniper weapon special ability. You can do this even with unwieldy sniper weapons.