If you have CMS licensing, that includes Deployment Server which includes Ghost. This means you are legally entitled to use Ghost on the machines you manage with CMS. The licensing is machine based.
This means you can't for example buy 1 CMS license, get the Ghost binary, and then use Ghost to deploy 1000 machines.
When we enquired about this the cost effective solution was to buy a DS site license (to ensure we were legal to machine every machine with Ghost if we wanted -whether from DS or not) and then buy CMS specifically for the machines we fully manage.
Does that make sense?