I don't think there is any reason to believe that character is anyone else other than Finn, other than the concept art shows him as not being dark skinned. It was likely created before the casting of John Boyega.
I just watched the movie again. When Rey and Finn start to climb the outside of the giant regulator building you actually see a quick glimpse of the snow-speeder they must have just used.
You can see where the deleted scene likely was. Han and Chewie enter the building, and then Rey and Finn are somewhere and manage to trigger all the doors to open. Next we see Rey and Finn outside the building (next to the snow-speeder) starting to climb. For some reason they needed to go somewhere else to open those doors, and then likely had a hectic race back to help Han and Chewie.
Boyega, who was born in London to Nigerian parents, went through seven months of auditions before being told he had the role and when it was announced he was the recipient of some racist internet bullying. But he responded by posting a message on Instagram telling those who thought there couldn't be a black stormtrooper to "get used to it." - telegraph.co.uk
Unless you believe the top and right images are actual footage.