RHEL 5.5 - RHSM - Fail to install subscription manager

Hello,

I need to update an old server that wasn't connected to the net.
Red Hat Enterprise Linux Server release 5.5 (Tikanga)

I need to register it to RHSM, so I tried to install the package subscription-manager (subscription-manager-0.98.14-1.el5.x86_64.rpm)

But I get:
rpm -i subscription-manager-0.98.14-1.el5.x86_64.rpm
warning: subscription-manager-0.98.14-1.el5.x86_64.rpm: Header V3 DSA signature: NOKEY, key ID 37017186
error: Failed dependencies:
python-ethtool is needed by subscription-manager-0.98.14-1.el5.x86_64
python-rhsm >= 0.96.11 is needed by subscription-manager-0.98.14-1.el5.x86_64
python-simplejson is needed by subscription-manager-0.98.14-1.el5.x86_64
virt-what is needed by subscription-manager-0.98.14-1.el5.x86_64

If I try :
rpm -i python-ethtool-0.6-5.el5.x86_64.rpm
warning: python-ethtool-0.6-5.el5.x86_64.rpm: Header V3 DSA signature: NOKEY, key ID 37017186
error: Failed dependencies:
libnl.so.1()(64bit) is needed by python-ethtool-0.6-5.el5.x86_64

Instead of dealing with the manual installation of all the dependencies, I'd like to use a local repository.
In a similar case, with a RHEL 6.1, I used the DVD installation .iso file as local repository to YUM all what I need for the subscription to RHSM.
I did it with this:
https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/5/html/deployment_guide/s1-yum-upgrade-system

And all was fine.

I did the same procedure on this server (RHEL 5.5), but when I yum update it, I get

yum update
Loaded plugins: rhnplugin, security
This system is not registered with RHN.
RHN support will be disabled.
file:///tmp_mnt_local_repo/repodata/repomd.xml: [Errno 5] OSError: [Errno 2] No such file or directory: '/tmp_mnt_local_repo/repodata/repomd.xml'
Trying other mirror.
Error: Cannot retrieve repository metadata (repomd.xml) for repository: rhel5.5-Server. Please verify its path and try again

And effectively there is no repodata/repomd.xml in the DVD's root directory (rhel-server-5.5-x86_64-dvd.iso) when this repodata/repomd.xml exists in the root directory of rhel-server-6.1-x86_64-dvd.iso file

Does someone have a solution to install the subscription-manager and all its dependencies easily or a solution to set the install DVD as a local repository.

Thanks