Interesting questions @Neo
In a physical universe wouldn't wars be conducted physically, real bodies, real tech, real weapons, etc, much like what happens here on this planet? There are physical assets and trophies in play.
That is not to say there is no mental/electronic warfare going on, which affects the physical targets.
Taking things further this raises an interesting question, can ISBE's out of body, influence and affect those in bodies? It sure seems so from many human ISBE's experience on planet, that can and does happen.
Wouldn't leaving a body in death and reanimating another require non bio bodies to jump from one to another? Physical bodies like we have here take time to reach maturity, so once the number of bodies are depleted, there's no immediate respawn back into the game as a ready to go fighting human unit. It has been how wars on this planet have been won, prior to the tech advancements we find ourselves in now.
There's indication the Domain also used physical reality assets to defeat the rogue element in our solar system. They used a large battlecruiser, and disc's, etc. All those physical assets need some form of physical personnel to operate them. So the ISBE's would have been utilizing bodies of various design that can operate in both a physical and space location.
There's some physical evidence to back up a portion of the book where the rogue element Mars base surface structure was destroyed. Davies Crater approx 300km north of Cydonia on Mars, certainly looks like blast radius and it is over 200km diameter. The Domain said they used electronic cannon as one of their weapons. If one was used at this location, it packs a punch so to speak.
There's an image of Davies crater here midway down the page https://www.ibtimes.co.uk/google-maps-take-virtual-tour-mars-moon-1460148
To add something else, I am not sure, but for example if an ISBE's disc was taken out, they were ejected from the body they used and they were operating within the effective traps area in this galaxy, would that mean they would be subject to capture and being imprisoned here? Or because they are not registered in the database, they aren't perceived by it? Alien Interview seems to suggest that ISBE's need to be processed into the system for it to work. The ISBE's at the Himalaya Base were processed at the Mars Base and then forced into the system, much like our prisons here inmates are captured, processed and held within the walls of the prison. Airl was able to escape because she was never captured and couldn't trigger the trap?
I don't know but some food for thought perhaps?