Warhammer 40k - Tau detachment benefit clarification

Question

Coordinated Firepower is a Tau detachment benefit:

Whenever a unit from a Hunter Contingent selects a target in the shooting phase, any number of other units from the same detachment who can still shoot can add their firepower to the attack. These units must shoot the same target, resolving their shots as if they were a single unit ... the firing models +1 BS

Independent character Darkstrider has this special rule

When Darkstrider targets a non-vehicle enemy unit with a shooting attack, that unit suffers -1 toughness against hits from that shooting attack - this applies to Darkstrider's entire unit, not just his own

Darkstrider can only join Fire, Breacher, and Pathfinder teams BUT if I'm reading this correctly, if I use Coordinated firepower, fire at a MC with Toughness 6 using 3+ units (let's say a tank, the pathfinder team w/ Darkstrider, and broadside), does the tank and Broadside fire at the MC using his 5 toughness, due to Darkstriders -1 T ability?

Basically the Hammerhead tank has a Str 10 railgun that would insta kill this 6 wound creature. From the bold items in the above descriptions, I'm thinking that they can?

However Darkstrider would have to be within a Fire, Breacher, Pathfinder unit for this to work. If he is on his own, he is not apart of the detachment.

edit: If this tactic works, then it's safe to say the same tactic would work with markerlights? That is, if I hit a unit with 4 markerlights, and 3+ units fire at that unit as a single unit, the markerlights apply to all units firing?

e.g. I use 2 marker lights for BS (so +2) and another 2 for ignores cover, usually I'd have to apply markerlights per unit firing, so if I shot with a unit of riptides and a unit of tanks, only 1 unit would confer the +2 BS & IC benefit. But if I fire with a unit of riptides, a unit of tanks, and a unit of broadsides, each unit gains the +2 BS & IC since they're firing as 1 unit (also the +1 BS for coordinated firepower).

Answer 1

With the errata* released in July of 2016, this is now a much clearer rule. The rule now reads that the shots are resolved at the same time, but does not indicate that the shooters are all counted as the same unit. Just like the rule read before, the benefit of the improved BS and shared markerlights still applies, but you no longer get to share unit-wide special rules. Darkstrider no longer confers the toughness reduction to all the shots in the coordinated firepower attack. A Commander with the Signature Systems that buff his unit if he does not attack no longer confers ignores cover and twin-linked to an entire coordinated firepower volley.

*GW publishes errata and FAQs on facebook first for comments, then pushes them to their site later. Bell of lost souls reposted them for those without facebook accounts here

Answer 2

Check the last GW Tau FAQ on their facebook page. They have errated this rule to read "They shoot at the same target one after another" rather than "as one unit". That ends the discussion.