Hi,
This works for me:
more inv.txt
dn: ou=ny\<group\>mmm,dc=redhat,dc=com
changetype: add
objectclass: organizationalunit
 ldapmodify -x -h localhost -p 1390 -D "cn=directory manager" -w secret12 -f inv.txt
adding new entry "ou=ny\<group\>mmm,dc=redhat,dc=com"
[ludwig@elkris ~]$ ldapdelete -x -h localhost -p 1390 -D "cn=directory manager" -w secret12
ou=ny\<group\>mmm,dc=redhat,dc=com
[26/Jun/2014:16:53:26 +0200] conn=9 op=1 ADD dn="ou=ny\3Cgroup\3Emmm,dc=redhat,dc=com"
[26/Jun/2014:16:53:27 +0200] conn=9 op=1 RESULT err=0 tag=105 nentries=0 etime=1
[
[26/Jun/2014:16:54:23 +0200] conn=10 op=1 DEL dn="ou=ny\3Cgroup\3Emmm,dc=redhat,dc=com"
[26/Jun/2014:16:54:26 +0200] conn=10 op=1 RESULT err=0 tag=107 nentries=0 etime=3