Around 2100 this evening the 10 beautiful monitors of the wall all went blank and looked like they were going to go into power saver mode, as if the signal from the computer was lost.
After a few moments, however, the RHEL7 login screen appeared, correctly spanning all ten monitors.
Logged in as user alarms, and got what is shown in Figure 1. All ten monitors are actually active, the mouse shows up on all of them when dragged across, but no background, window titles (aka dressing), only JMenu and few desktop icons in the top left-most monitor. Able to right-click and open a terminal.