Generally digital signals are broad band and redundant. The spark gap hits all bands, but not all bands at once. Noise would affect a few 10s of bits per seconds, but if you are sending out 10,000 bits a second, and you have cyclic redundancy checks to both detect and correct any errors, you mostly can ignore the jammer.
If they put 10,000 spark jammers out there, they would be likely to hit the same bits multiple times, rather than just hit the ones they missed. Further, a jammer is a beacon. If you broadcast vs. the US, you may have a loud noise coming your way.
I understand frame relay etc...
and yes jammers draw attention !
But I dont think Harm/Alarm/Sidearm/Standard could focus on it. but LGB / Iron / cluster could do the job.
lol...