https://www.law.cornell.edu/cfr/text/32/553.32
section c., specifically. note that there is not a carve-out here as in section b., "other than official ceremonies;" i.e., the letter and the spirit of the law are abundantly clear that no partisan activity can be held there, with no exceptions.
the Trump campaign has indisputably violated section c., and has provided irrefutable evidence thereof on social media.
as well,
(8) Filming or photographing will not be permitted if it conveys the impression that
cemetery officials or any visitor or family member is endorsing any product, service or
organization. Additionally, ANC will not authorize any filming for partisan, political or
fundraising purposes, in accordance with the Hatch Act, 32 CFR 553, and AR 360-1.
https://www.arlingtoncemetery.mil/Portals/0/ANC-media-policy.pdf
Whether they and his crew broke the law, or the spirit of the law, the larger question is what is wrong with people these days, even that family, such poor taste and impropriety. And then his defense team ...wow!