I believe ePO will identify this through registry values and OS installed on those machines.
You can review the properties for servers and workstations to see if they're correctly identified.
If by some chance you have a physical workstation (a hardware that is intenteded to be used as a workstation) with Server OS installed, ePO problably will identify this as a server.
Then, you can configure policies for server and workstations, note that you don't have to create a policy for each one. The same policy can configure specific settings for servers and workstations.