First of all, I'm afraid this is a wrong forum (you should have used WebCenter Content).
Secondly, I'm not sure I understand the question.
a) Physical items are a URM-only feature
b) A physical item - as you can see here http://docs.oracle.com/cd/E23943_01/doc.1111/e10789/c06_phy_content.htm#g1235872 - is a "metadata-only" item, which has some specific characteristics (e.g. chargebacks http://docs.oracle.com/cd/E23943_01/doc.1111/e10733/c09_chargeback.htm#g1108926 or reservations http://docs.oracle.com/cd/E23943_01/doc.1111/e10733/c10_reservations.htm#g1313375 )
c) URM has all the features of UCM's Content Server - therefore, you may define your own custom metadata
Now, when you mention UCM, do you mean a different server (running on a different port than URM, having its own data model in the database), or do you mean UCM's core features? Furthermore, if you mean a different server what is the relationship between the UCM and the URM servers; especially, concerning physical items?