I don't know about FOIAing the DHS/FBI to see if they're "targeting" KF through the ISPs. It's pretty obvious #DropKiwiFarms is led by individuals with connections mainly in media and IT, not LE per se. As for the Fedz I am sure they must have a huge dossier on KF by now, but even if they did, what can you do about it? The situation at Twatter is very different from the one at KF and I don't think the two are remotely comparable in any way. Twatter were actively in dialogue with intelligence and granting the FBI/DHS whatever censorship requests they submitted. Twatter were allowing themselves to be manipulated by intel about supposedly impending disinfo campaigns, which made them more willing to grant whatever censorship requests came in from the government. There's always a lot of speculation all over KF about "glowies" being agents provocateurs on this forum, but the fact is that you can't conclusively prove any of that, and even if you did, there isn't much you can do about it to prevent it. I suspect the idea of the Fedz having a huge secret folder on KF that could or couldn't be FOIAed is very sexy to a lot of people, and would make KF seem like a huge deal in a lot of people's minds ("Oh look even the FEDZ are paying attention to KF!") but it's all quite pointless in the end. The government can build themselves an army of paper tigers that the average person is ultimately powerless against.
On the other hand #DropKiwiFarms have implied they'd FOIA the FCC to gain access to any complaints filed against ISPs by KFers in order to doxx KFers using those letters:
Edit:
OldManLondre, the Youtuber
who has been targeting KFers' crypto addresses to get them shut down, he announced he was going to FOIA the Fedz for any records on KF: