Can you export or share Categories in Outlook 2011?
Sadly, and unfortunatly No. This is something I spend a few days on recently, and out of interest, it can't be done on the Windows version either. There is no way to keep these categories intact, and it can be a huge problem, especially when sharing items with others since the minute they make a change to a shared item, the categories are overwritten.

You could possibly however use an AppleScript to add them manually, I haven't tried thought.