Control surfaces that connect to the computer via USB or Firewire don't present their midi connection buy name to Digital Performer, because Digital Performer recognizes them as an "interface" and not a device connected to an interface.

Go to the MIDI Devices tab in Audio Midi Setup. If drivers are installed correctly, or the device is class compliant, it should automatically show up in this window and will have ports on the bottom of the icon, like a interface would have.

Click Add Device and set the properties of that device for your control surface or the type of surface that it's emulating, such as a Mackie Control Universal, or HUI. Then connect the In and Out ports on that new device to the ports on the bottom of your interface in the window.

Then, that new "fake" device will show as you MIDI port choice in the Control Surface Setup of Digital Performer.