"Only Rebel soldiers who laugh at danger may join the Jetpack Troopers. They hurtle over walls and attack targets head-on. Hovering mid-air, they are safe from Mortar Turrets but vulnerable to direct-fire weapons."
~In-game description of Jetpack Trooper
Jetpack Troopers are units that fly over walls and can attack targets inside a base. They can not be hit by Mortar Turrets but can be hurt by direct-fire from other turrets, such as Burst Turrets, Rapid Fire Turrets and Rocket Turrets.
Since Jetpack Troopers hover, they only set off IDT Traps (Imperial) and LAAT Traps (rebel).