The short answer is that the Outer Space Treaty states that all commercial satellites are under the jurisdiction of the country in which the company exists, regardless of where they are launched. SpaceBees is a California based company, so the US government is the ones they answer to, not the country they hired to launch their stuff. Since satellites must communicate and could potentially disrupt the communications of others, the FCC gets a say in what goes on. The FCC is not the only authority in town, just the ones taking action here.

As far as satellites with covert missions or missions other than what is publicly stated, we should probably assume they already exist. The NRO is pretty sneaky and the USAF has never stated what the heck the X-37 is doing. There's a good chance that they have other satellites with publicly acknowledged missions that are doing something else behind the scenes. They are probably attempting to guard against that same behavior from others as well.

Doing optical imaging probably isn't feasible for a cubesat, it takes quite a bit of fuel to get next to another satellite and not hit it, so a cubesat can't zip up to dozens of satellites to get detailed images with a smartphone size sensor- it would run out of fuel too quickly. Instead, optical satellites will probably have their own orbit and accept that they will be far away from their targets. Large distances require a huge aperture if you want a good image, but it's not hard to imagine a satellite such as Hubble occasionally rotating to catch an image of Russian or Chinese tech. Plus, the NRO has sent up several very large payloads that we don't know what they do, so there's probably a large aperture imaging satellite snapping images we don't know about. What cubesats can do is extend long antennas that were folded up for launch. A small cubesat could be effective at RF surveillance and a constellation of cubesats and good signal processing could provide a surveillance system for other satellites that could spot various communication types and record the orbital information of the satellites doing the transmitting.