The ranged weapon options are pretty limited (Tac Bow, Combirifle, and a MULTI Sniper), and with BS11 the Ninja will struggle in gunfights even with its TO camo. Instead, the Ninja's best weapon is an active turn CC attack; but even that is a risk. Offensively, the sniper profile, infiltrated into a hidden deployment position will be the most dangerous threat, but your army likely has better long-range tools that won't risk an expensive specialist slot.
A killer hacker is a strong mid-field specialist able to infiltrate next to an objective or drop 30 points in an important zone. It can also clear an area for heavy infantry to move up into a threat position. Consider placing it in hidden deployment and revealing on the second turn to hop onto an objective.
Ultimately, the Ninja is a weak TO specialist that is expensive to field. Use cheap template weapons to threaten its position, or MSV to negate its camouflage. Ninja will crumple under a sustained threat.
Ninja should infiltrate up to the midfield in total cover or in hidden deployment. Specialists should be close enough to strike at an objective, but shouldn't be at risk of the enemy.
Avoid attempting the superior infiltration roll, and don't place the Ninja in an ARO position.
Active Turn Role
Very limited. Avoid if at all possible.