it is made by same artist who made the trucks in the game. i have seen his work, he usually makes highly detailed big projects like that if he is being contracted to work on something. normally he makes smaller stuff for fun/hobby. so i have reasonable suspicion that although the logo might be added on, they have plans for those vehicles anyway. also, i found those pics from his artstation website. those logos were there already. maybe he is playing, but some of the stuff looks familiar:
https://www.artstation.com/artwork/4LNv8
as you can see, he does not randomly put logo, he puts logo on things he actually works on for spintires. here is one of my favorite trucks in the game. has spin tires logo:
https://www.artstation.com/artwork/81Lbq