techblog 

Some time you may have a requirement to copy an ORACLE_HOME from one location to another using OS level commands. However, one thing this will not do is update the Oracle Inventory. Having an incomplete Inventory will screw up any attempts at subsequent patching of this cloned ORACLE_HOME.

oracle@bdb ~]$ opatch lsinventory
Invoking OPatch 10.2.0.4.2

Oracle Interim Patch Installer version 10.2.0.4.2
Copyright (c) 2007, Oracle Corporation.  All rights reserved.

Oracle Home       : /opt/oracle/product/10.2.0.2
Central Inventory : /home/oracle/oraInventory
   from           : /etc/oraInst.loc
OPatch version    : 10.2.0.4.2
OUI version       : 10.2.0.2.0
OUI location      : /opt/oracle/product/10.2.0.2/oui
Log file location : /opt/oracle/product/10.2.0.2/cfgtoollogs/opatch/opatch2008-02-08_11-58-44AM.log

List of Homes on this system:

  Home name= OraDb10g_home1, Location= "/opt/oracle/product/10.2.0"
  Home name= OraDb10g_home2, Location= "/opt/oracle/product/11.1.0"
Inventory load failed... OPatch cannot load inventory for the given Oracle Home.
Possible causes are:
   Oracle Home dir. path does not exist in Central Inventory
   Oracle Home is a symbolic link
   Oracle Home inventory is corrupted
LsInventorySession failed: OracleHomeInventory gets null oracleHomeInfo

OPatch failed with error code 73

Oracle clearly support the ability to clone an ORACLE_HOME as the oui installer has an option to attach a cloned home to the Inventory:

 runInstaller -attachHome ORACLE_HOME="/opt/oracle/product/10.2.0.2" ORACLE_HOME_NAME="ORADB_102"

After you have attached the cloned home you can quite happily apply interim patches and patchsets to your newly cloned ORACLE_HOME.