I have a Sprint 8130 on a BES. There are some items that show up on Outlook that I can't get to show up on the 8130 Calendar. There ARE conflicts (it's airline info, hotel, rental car etc for a trip) but on a similar trip in a few months, everything is showing without problems, despite the same type of conflicts.
I've tried a battery pull, as well as changing the theme to no avail. This hsn't been a problem before. If I add something to the 8130, it shows on both with no problem, but don't want to have to manually do everything.

Any ideas?

Try resending the Service Books from the BES server. If you don't have access to do this then have your BES admin do it. Not sure if this will fix it but that's my two cents. Someone with more BES experience can probably chime in and give a better answer.