The SQLSvc account is the core account that CallManager uses to do the things it needs to do. If the passwords are not correct and synchronized between servers, then all kinds of services will not start and subsequently things don't work correctly. The sa account gets used during installation and migration and is otherwise rarely used by the system. I have changed the sa password on the publisher and then on subscribers so they match and have had no problem.
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.