I honestly don't see why DTM 4.2 SP2 couldn't find any OUTLOOK Calendar folders even if Outlook was used to access another calendar database. Now the only time you'll have synchronization of "emails" is if your BB is tied to a BlackBerry Enterprise Server (BES) through work. Otherwise DTM 4.2's "Synchronize" program only syncs 4 items (Address, Calendar, Memos & Tasks). When you initially configured it, had you been making sure to select the folder that the Calendar information was in (like OUTLOOK/CALENDAR maybe)?
Does the Oracle Connector put the calendar entries in THAT default folder location in Outlook or some other type of sub/remote folder?
Just a thought when you mentioned (MAPI). From what I've dealt with concerning MAPI profile settings when dealing with OUTLOOK, the MAPI profile settings may have to be looked at at some point if you haven't done so already. It might not know yet which profile to be under in order to find that calendar folder that the Oracle stores the entries in. It just sounds to me like that folder is somehow either beyond the DTM's reach to get into or it's set up under a profile that doesn't match up with your Outlook profile.
Oh wait, I did a search on the BB Knowledge Base and found this specific link to your question: BlackBerry Search Results
Apparently the Oracle Connector (no matter what DTM version) is not a supported application dealing with the MAPI profile (which is what I thought would be involved). I'm sorry to say but you may have to continue doing the work around unless you're able to get something where by you can have that info automatically transferred into a strict OUTLOOK MAPI PROFILE setting that the DTM can find.