[templar]

After that, though what do observers have to work with besides radio traffic and radar?

Telescopes (maybe earth or lunar orbital ones)? The moons terrain would be highly disturbed by any work done there. No vegetation or overgrowth to conceal it.

[RightWhale]

Yes, upcoming moon orbiting satellites would make surface operations kind of exposed, but we have earth observing satellites already and still don't know for sure what is going on in various hostile countries.