The Stealthsuit Team is the "lone wolf" of the Tau Empire's military and are the equivalent of Space Marine Scouts or any similar unit.
Equipped with either the XV15 or the newer XV25 Stealthsuit, these teams operate independently from other military formations. In fact, they are not usually factored directly into Tau battle plans, and so enjoy an unusual degree of freedom within broad mission parameters, with team leaders gaining a reputation of eccentricity as they employ unorthodox tactics. Operating in teams of three to six members, including the team leader, their primary role is to ambush isolated enemies and act in support of friendly units, often ranging far ahead of the main Tau army. Examples of this include the Taros Campaign, where Stealth teams were able to almost consistently attack imperial convoys full of water, munitions, and supplies, forcing the Imperium to concentrate forces to try and protect these formations, leading to fewer units on the front lines, meaning fewer units to fight the Tau. In short, they lost the war of Attrition. They also played a minor, albeit important harassing role on Imperial armor during the Damocles Gulf Crusade.
Stealthsuit teams do sometimes play a more integral part in planning and executing a mission - i.e., when acting as part of a Rapid Insertion Force.
In addition to their jetpack-equipped Stealth armour, each member is armed with a Burst Cannon, and all may take one Battlesuit support system. Members may also replace their burst cannon with a Fusion Blaster, though no more than two are allowed in a full six-member team. The team leader may also swap his Burst Cannon for a Fusion Gun and if he is of Shas'vre rank, he is allowed a markerlight.
Stealthsuits are now cheap , and basically a lite Primaris Marines. With an inherent -1 to hit at all times, this makes them heavily viable, even in melee combat so long as the things you charged have basic CQC weapons and not Eviscerators or powerfists. They are harder to wound than their Fire Warrior bretheren, being lite marines and all.
However, they really shine when they have their suit systems thrown on them. Most builds will have ATS thrown onto them to give Burst cannons some extra mulch power, while another system is usually given to the Guy with the Fusion blaster. Velocity tracker is generally the cheapest and most utilitarian. The Shas'vre can take a target locked, markerlight, and another system.
Under dedicated Firepower Stealth teams will crumble, but that's not their job anyway. Their job is to harass, and get into positions to bring Crisis suits into Melta range with their Fusion weapons. In a jiffy they can serve the role well for mainline combat, but really they serve mostly for objective holding and harassment.
It is possible to take two Shield, Gun, or Marker drones with them. The drones are best left behind, as your team has other things it can be doing than worrying about drones.