Over at StarWars.com they've revealed the character's true name is FN-2199, nicknamed "Nines" and is a riot control officer in the First Order, hence the baton weapon he wields. David Acord, a sound editor from Skywalker Sound, gave FN-2199 his distinct voice. The character actually debuted in Greg Rucka's novel, Before the Awakening, in which he trains and fights alongside Finn. Here's a look at him sitting in the background with bright red hair...
The site adds...
"There’s a reason that Nines gets to use an awesome weapon (which is called a Z6 baton). He’s riot control, and part of an elite squad that enforces order or squashes uprisings. While their weapons are non-lethal in theory, the Z6 can definitely cause harm or kill an opponent when used with brute force."
Pretty cool, and Disney has been going out of their way to make the new Star Wars canon feel truly cohesive. Besides this, the Resistance pilot played by Greg Gutfield was revealed to be Temmin Wexley, a character who plays a prominent role in Chuck Wendig's book, Aftermath.