The current licensing structure is for all UM or all VM licenses on a key (i.e. on a single Unity server). This doesn't have anything to do with what's technically possible, it's a sales/licensing thing. Annoying, I know, but there's no ability to have both UM and VM license counts on the same Unity box at this point. Not sure if this will change for 4.0 or not (I don't think it will).
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.