Disable Display Port output during Linux upstart (boot)

We have an interesting hardware configuration where we will have a single monitor connected to the same host with several X-servers running once the machine has finished booting.
If the display port is active during Linux upstart, the monitor detects this signal and will make that the active display (which at this time is a small underscore in the upper left-hand corner of the screen).

Running RHEL 7. Hoping that there is a grub option that can accomplish this.