Of course they can be jammed, it's just harder and needs more power.

In the military cat and mouse game I don't think it will be an issue. Maybe that is why fibre was adopted instead.

It absolutely can be jammed, the same way other frequency hopping radios and systems can and do get jammed.

Civilian telecoms are absolutely used in military UAVs. Ukraine and Russia both use their opponents SIM cards in long range strike drones. And I’m pretty sure that attack vector would work well anywhere, including the US.