Did your Ubuntu install come up with a GUI - if so displays are likely controllled by a progran called xrandr which enables dual sceens, setting graphics resolution, which is primary screen, whether screen 1 is to the left or right of screen 2 etc. You can even make up your own screen resolutions within reason...
An idea or two...
1. Use vnc and remotely control the install. Seach "install centos 7 using vnc"
2. Use a rs232 port and serial terminal or PC with terminal program. Search "install centos 7 using serial terminal"
3. Use a kickstart file see for example Kickstart
No idea whether the code do this has been retained by ClearoS and works. Also the first two will require supported ports and drivers for NIC or RS232 port.
4. Do an Ubuntu install to find the NIC and Disk Drive hardware and the loaded drivers to support them. Find a machine which has a working display during CenOS install and which has hardware that will load the same NIC and Disk Drive drivers. Install ClearOS on the compatible machine, then remove the drive and install in the odd-ball machine. It should boot and use your dhcp server log to find the ip address assigned, or assign a fixed ip address before moving. You should then be able to control remotely from another machine over your network.
5. Install Ubuntu, or any distribution that installs to a GUI with output you can see, and install and run ClearOS in a VM