TEXT: Chapter Approved – Codex: Tau Q&A (v2.0)
  Q. Is it possible to make cover saves against markerlight hits?
  A. Markerlight hits do not permit cover saves.
  Q. Do markerlights function like searchlights at night?
  A. Markerlights are not searchlights and have no special value at night.
  Q. When Pathfinders make their pre-game free move, can their Devilfish
  transport move as well? Also, can they move in the Devilfish?
  A. Pathfinders’ pre-game free move may include their Devilfish transport. The
  move is performed as normal and may include embarking or disembarking.
  Q. If a target is hit by a markerlight, can any friendly unit see it to fire on it?
  A. A unit that fires at enemy that has been hit by a Markerlight must still be able
  to draw a line of sight to engage it, unless they are firing a seeker missile or
  smart missiles. This includes being able to see it if Night Fight rules are in effect.
  One weapon may be fired, hitting on 2+ for each markerlight hit.
  Q. Does a searchlight have any effect on a Stealth team?
  A. If a Stealth team is observed by a vehicle with a searchlight when the Night
  Fight special rules are in effect, any subsequent attempts to spot the Stealth
  team that player turn, test as if it were daylight.
  Q. Is it possible to hide behind a Stealth team which blocks line of sight by
  being in base-to-base contact?
  A. Stealth teams never block line of sight to other Tau units. Similarly, an
  Independent Character cannot claim to be immune to enemy fire by being within
  6” of them or by joining the unit.
  Q. Can Tau pulse rifles rapid fire at up to half their full range?
  A. In accordance with page 57 of the rulebook, close range for all rapid fire
  weapons is 12” so obviously this applies to Tau pulse rifles.
  Q. If I field a Tau Crisis team consisting of a lone warrior, does he always
  have to take ‘All on your own’ tests?
  
  A. All on your own tests only apply if reduced to a single model by casualties, not
  if you start that way, so one man Tau Crisis or Broadside teams do not have to
  take ‘All on your own tests’.
  Q. If I move 6” with my Devilfish and fire its burst cannon, can I also launch
  any of the seeker missiles it is carrying?
  A. Seeker missiles can be fired in addition to a vehicle's other weapons, even if
  the vehicle has moved more than 6”.
  Q. When a Tau Crisis team enters the table via Deep Strike, can they move
  in the Assault phase?
  A. Tau models with jet packs may not take their 6" Assault move if they Deep
  Strike.
  Q. Is a vehicle with a disruption pod any harder to see at night?
  A. Disruption pods do not affect visibility. Range and visibility are different things.
  Firstly, check whether you can see it. Secondly, check that it is in range.
  Q. If a model has a markerlight and a Tau jet pack, can it move and fire the
  markerlight?
  A. If you give the Stealth team leader a Markerlight you may fire it when you've
  remained stationary in the Movement phase, then move in the Assault phase
  using the Tau jet pack.
  Q. Can you clarify whether enemy characters (able to allocate hits in close
  combat) can ignore drones in close combat and strike other Tau they are in
  contact with?
  A. If drones are in close combat along with other Tau models then opponents
  must attack the drones if they can. If, for example, there is a Space Marine
  Chaplain attacking a Shas´o with one Shield Drone and the Chaplain is in contact
  with both models, he must attack the drone as it will seek to get between him and
  the Tau.
  Q. If a Fire Warrior team leader has a markerlight must he still fire at the
  same target as his unit?
  A. Yes, unless he also has a target lock.
  Q. Where a cost is specified for a single and a twin-linked weapon, is the
  twin-linked cost for one or both weapons?
  A. Both.
  
  Q. Could you confirm whether Tau Fire Warriors or Kroot block line of sight
  to Crisis and Broadside battlesuits.
  A. Both Fire Warrior and Kroot models are more than half the height of the
  battlesuits so in accordance with the Warhammer 40,000 rules they will block line
  of sight if arrayed base-to-base. Note that separate units of Gun Drones will no,t
  as the height of the flying base is not considered. This latter ruling is a change
  from earlier statements, apologies to anyone inconvenienced.
  Q. If a Tau commander is accompanied by Drones can he be targeted as a
  separate unit.
  A. Yes he can, because of this the Commander should try to join another unit to
  avoid being picked on.
  Q. Is the range of smart missiles limited when the night fighting special rule
  is in effect?
  A. No as stated smart missiles do not require line of sight.
  
SOURCE: textdata/thevault/Warhammer/40k/1st-8th Editions (Prior)/Errata/Warhammer 40k - Errata - Tau QA.pdf