At this point full multi tenant support (which means a lot of things to a lot of people) is not on the short term radar - you can get reasonably close with Unity 4.x, however. You may want to check out the "Audio text applications in Unity" doc out on the Documents page of www.CiscoUnityTools.com - I talk a little in there about what you can (and can't) do with regards to supporting seperate customers on a single Unity deployment which may be helpfull.
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.