Have a look at hese docs, hopefully they will help clear things up for you.
About License Requirements for Failover
When Cisco Unity is configured for failover, the requirements for system keys or license files vary depending on the Cisco Unity version installed.
Cisco Unity Version 4.0(x)
License files are installed only on the primary server. The Install License File wizard extracts the license data from the license files and stores the license data in the UnityDb database. When you run the failover configuration wizard on both the primary and the secondary server, the license data in the UnityDb database replicates to the secondary server. When this replication occurs, all of the features enabled on the primary server are enabled on the secondary server.
When you run the failover configuration wizard, it makes the license files available to the secondary server. If you do not run the failover configuration wizard on both servers, the secondary server cannot access the license files from the primary server and therefore is not enabled. Installing license files on the secondary server has no effect and does not enable any features.
Without contact with a primary server (and its license files), the secondary server will continue to function for a limited time. For licensing restrictions on using a secondary server without a primary server, refer to the "Licensing Restrictions on Using a Secondary Server Without a Primary Server" section in the "About Cisco Unity Failover" chapter of the Cisco Unity Failover Configuration and Administration Guide, Release 4.0 at http://www.cisco.com/univercd/cc/td/doc/product/voice/c_unity/fail/fail401/ex/index.htm.
From this doc;
White Paper: Licensing for Cisco Unity (All Versions)
There is only one license that is provided for failover systems, and it goes onto the Primary Cisco Unity server. If you open the license file with Notepad, you should see the field LicSecondaryServerIsLicensed is set to Licensed. This helps ensure that you are correctly licensed. Refer to the Installation Guide for your specific release, for instructions on how to install failover. After installation, Configuring Cisco Unity Failover provides additional detail.
As a confirmation, pull up the licensing applet on the Secondary server. It should display the licensing information that is present on the Primary server.
Are you getting this error “Installer User Interface Mode Not Supported. The installer cannot run in this UI mode. To specify the interface mode, use the -i command-line option, followed by the UI mode identifier. The value UI mode identifiers...
The below trick might come handy when you have to add a new node to a cluster but you don't have or is unsure of the security password for the publisher. This procedure has been around for ages.
1) Login into the CLI of the Publisher.