I don't have any issue with CG creating a character from thin air, just as long as they add to the lore. He's not a main character, but him just "being there" on Endor would be pretty lame. A couple o...
Just to nitpick, it's not just that he's missing a finger: his whole right arm is shorter compared to the left, it appears to be some form of radial longitudinal deficiency.
I'm not saying that disqualifies him from participating in a desperately under-resourced and under-staffed Rebellion taking place in a fictitious universe.