Based on the RR and SW:L Official Rulings:
QuoteQuestion: When a unit performs a ranged attack, does the unit leader need to have line of sight to the defending unit?
Answer: No. While range is always measured from an attacking unit leader, the unit leader does not need line of sight to a defending mini in order for the unit to perform an attack. However, only minis that have line of sight to a defending mini can contribute a weapon to the attack pool.
and
QuoteQuestion: When attacking an enemy trooper unit that has a face-up order token while the command card Reckless Diversion is in play, can the attacking unit form one attack pool for the enemy trooper unit and form a second attack pool in order to attack a different unit?
Answer: Under most circumstances, the attacking unit cannot do so. The attacking unit, and each mini in that unit, must add all eligible weapons to the attack pool that is targeting the enemy trooper unit with a face-up order token. A unit, or mini, cannot "choose" a weapon that is not eligible to be added to that dice pool if it can add a different weapon that is eligible. The attacking unit can only form a second dice pool if, after first forming a dice pool with all eligible weapons, there are still weapons useable by the unit that were not eligible to be added to the attack pool targeting the enemy trooper unit with a face-up order token.
is the following legal or illegal?
Grey Box : Line of sight blocking terrain
Green: Rebell Squad with face up order token from Reckless Diversion.
Blue: Rebell Squad
Red: Snowtroopers with flamethrower.
" C " being the squad commanders.
(R1 and R2 are range 1 and range 2)
Red declares intent to use an attack action. Red is forced to chose range 3 weapon to attack green. Remaining squad members can't add their dice to the attack pool because they don't have LOS.
Thus they are allowed to form a different attack pool to attack blue with flamethrower and possibly grenades.