It's very hard to prevent the LO from leaking into the ADC input. Putting the filters in the right places would cause a lot of issues for the signal chain so a common workaround is trying to null it with a 180 degree out of phase LO signal.

I don’t know all the details of this kind of technology, but I would imagine that one direct RF receiver’s sample clock looks effectively identical to any other similar receiver’s sample clock. So if these devices become popular, then a military sample clock is indistinguishable from a civilian sample clock. In contrast, an LO is rather application-specific.

For military use, where you are trying to blend in with civilian equipment, either the direct sampling clock, or the local oscillator frequency, could be randomly chosen in quite a wide range at bootup and still have the device work.

In todays world with everything software reconfigurable, changing the sampling rate or local oscillator frequency is very do-able.