I used to do this kind of work in the 90s, and the requirements from a monitor & command workstation are quite different from an ordinary desktop system (and that's probably why they all had support laptops nearby).
First of all, the window manager is just there to provide, you know , window management. There's no application functionality like file management or anything like that built in. You have a WM (I used Motif 1.2), a base toolkit (Xt) and then you expand that with homegrown controls.
The point of having little extra functionality is to reduce the overall "attack" surface of the workstation; security is not a primary concer here, but process interactions and active tasks should be kept to a minimum to increase the responsivness of the system.
Real time requirements are also not high in the list, as these workstations provide monitor & control functionality only. It should be possible to completely yank them from the system and the mission should not be affected in the least.
That all leads me to think that no, it is probably not Gnome