It's different only in licensing. As I see it, most licenses are issued thru a government agency to either a private/semi-private/or government owned but not run ATC service provider. The FAA is the regulating government agency for ATC in the US AND by far the largest service provider therefore, it doesn't need to issue licenses for its employees. The military branches & DOD in the US are like the FAA in they don't issue licenses for the same reason, they are government run ATC. The only ATC licenses issued are for towers, many of which are contracted out and not being run by the FAA. And just to muddy the water, the FAA licenses to a few military run towers. My best guess it that just about every military tower works civil aviation at some point because we have so few restrictions on VFR traffic.