Apparently, the vehicle bonus codes can be shared.
To use these codes, pause the game, hit RB till you come to the Options tab, then go down to Bonus Codes. You must enter the numeric code using the onscreen buttons. This screen will also show you all code unlocks you've used.
18041851 - Vehicle: Warrior
18021974 - Livery: Butterfly
17121973 - Livery: Lightning Bolt
48992519 - Camo Army Helmet
20061977 - Road Addict Jacket
91031985 - Speed Angel Shorts
Thanks to
https://www.trueachievements.com/Silverace010.htm and electrofunkdaddy of x360a for the codes I didn't know.