Hmm, I've just tested and this is working for me. It sounds like you've already been through the obvious stuff:
- You can see the new calendar in iCal, therefore the CalDAV account is configured correctly both in OmniPlan and in iCal.
- Check that the resource filters actually return results by applying them to the Gantt view.
- Make sure that iCal is actually set up to display the calendars in question
- Refresh iCal using the menu item Calendar -> Refresh All.
If that doesn't work, maybe you can work directly with our ninjas? Your test document and any information you may have about your CalDAV server (Is it the Mac OS 10 Server one supplied by Apple?) would be helpful.
-Tom