I wrote this kludge tool a while back that will find the duplicate user names that exist in a tree in different OU's.
Usage is pretty straight forward. Copy the Jar file into a directory then type:
java -cp DupSeach.jar dupeFinder <host name> <login dn> <password><search filter> <search Attribute> <output filename>
<host name> is the hostname or IP address of the LDAP server
<login dn> is a user with rights to browse the entire tree
<password> password of the user
<search filter> LDAP search filter, in case you want to search onlyusers or something
<search Attribute> the attribute you want to search (CN or UID)
<output filename> the name of the file you want to write duplicates to
Example: java -cp DupeSearch.jar dupeFinder fs1.Acme.com
"cn=admin,o=Acme" secret "(objectclass=*)" CN "c:\temp\duplicates.txt"
You must have Clear Text Passwords enabled on your LDAP Server.