The Special Forces squad (AKA the "super soldier squad" in the png) is a set of skins selectable by the player when at the Soldiers section. They are allied with the Strike Force but are not seen in the Campaign, only in Challenges.
The medic skin looks much like the normal medic, with the only differences being white armor and a yellow riot mask. The assassin skin looks very different, it being a white and tan ghille suit with a white face mask and hood, making it impossible to see his face. The commando skin looks the same, except for its white and grey camo scheme. The helmet, called the "super soldier helmet" is also white with a blue visor. It is referenced in SFH3 with the achievement "Heads up!". The tank armor looks much the same as normal, but white, except for the helmet, which looks like a stormtrooper's helmet from Star Wars. The helmet of GlobeX tank, also shares the resemblance, who could be a reference to the black home hole trooper from the Star Wars EU.
You also play as the Special Forces squad on the mission Self Experiments, where you have to steal info from a team of buffed scientists.