Is there a requirement to have a valid ZPM subscription for every device known to ZCM?

In older versions I remember the license count being metered. If you only had 50 licenses and 100 devices, it would only work for devices which got a license assigned.
Is this still the case? I know that in older versions you could disable a device to free a license.

For example:
A customer has 250 workstations and 30 server.
The ZAA is installed on all of the devices.
The ZPM part of the ZAA is only installed and therefore used on the workstations.
The server folder is configured to not install the ZPM part of the agent.

Would it be valid to only have a 250 device subscription?
Does anyone have any links to pages documenting this?

Thanks & Regards,