Does anything in RAGE's multiplayer mode unlock anything in the single-player campaign?
Solution 1:
I haven't played much multiplayer myself yet, but extensive searching has turned up nothing so far.
So far as I know, multiplayer mode doesn't unlock anything in the single player campaign.
Solution 2:
I do not think it does.
Multiplayer cooperative is a bunch of side missions that you hear mentioned in the main story. The versus games are 6 man vehicle based matches.