I don’t believe that there is any functionality within business objects to accomplish this. My question is why are you wanting this? Generally once you have your object built and reports on that universe you don’t remove the objects so you shouldn’t really need to determine what objects are being used in the reports from a global level.
However, that being said, a quick search revealed this post
Where someone apparently developed java code to achieve what you are looking to do.
Hope that helps.
erik.stenson 
(BOB member since 2012-07-30)