Jason was a minor character who, on numerous occasions, aided Pickett, Ben and Ryan Pryce on various tasks against the 815 captives. He was once termed one of the ten trustworthy minions of Ben. Even though he was in the midst of several missions against the 815 captives, he did seem to be slightly different - - - he appeared to have a conscious.
During Season 3, he was first seen assisting Other named Michael in the Hydra operating room as Ben tried to convince Sawyer that he was in control. Jason told Sawyer to bite down on a stick to manage the pain while he held him down during the operation (which allegedly included planting a mini-bomb in his chest which turned out to be a hoax) and at the time Ben discussed Sawyer's fate at the Hydra Island lookout point.
Jason also assisted Jack at Colleen's funeral.
When Ben in surgery with Jack, Jason tried to convince Pickett, who was assisting, not to leave the operating room to go kill Sawyer. Jason went with Pickett to the cages, but instead of killing Sawyer, Pickett and Jason were beat up by Kate and Sawyer and left in the cages. Once they got out of the cages, they went to the beach to try to capture Kate and Sawyer, but they were unsuccessful.
Jason was one of the men who raided the 815 beach camp. Jason survived the initial ambush explosions to help capture Jin, Sayid and Bernard. As they were lined up on the beach waiting execution by Pryce, Hurley drove the van through the jungle striking the Others. Sayid tripped up Jason to the ground, then broke his neck to kill him.
However, several days after Jason's beach death, he is seen at Richard's camp. Ariston Green, the actor who played Jason, admitted in an interview that he was the person in that scene.
It was probably a production issue where the director needed background members and Green was available. But some would think that the producers and director would have known they killed off a character before this shot - - - which could lead to viewer confusion.
But one of the oddities of series was the strange "reincarnations" of certain characters on the island. Patchy was the prime example as the mad Russian got killed several times over but seemed to reappear to take revenge on the castaways.
But Jason reincarnation could have been a "reward" for not being purely evil, but just a foot soldier taking orders. That view would give the show at a least a partial moral fiber to the actions and consequences of some actors. If you have some morally positive attributes, you could be saved from final judgment or given a second chance in your island life.