As far as I know that service is only used for message transport via x.400 to Ex55 servers in the site - there may be more to it than that, but I don't think so.
this doesn't have anything to do with Unity - those errors are probably the system monitor stuff - you might check under the Exchange System Manager (to to tools | Monitoring and Status | Status - right click on the server name in question and check properties) to see if the service is listed as required or something. You can remove it as a dependant service here but I'm not sure about that.
either way, you'll probably want to check with the MS folks about this, not us - this is outside the realm of Unity.
One thing that does use the Exchange MTA is the Voice Gateway 2000. So if you're using AMIS, Bridge, VPIM or SMTP networking you don't want to disable this service on any server running the Voice Gateway 2000.
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.