Though I guess the loop hole here is that the National Guard would in this case be acting under "state authority" given that typically state-like actions for DC are deferred to Congress. The open question being whether the Executive branch could act independently, or whether they still need explicit authorization from Congress.
"The Act does not prevent the Army National Guard or the Air National Guard under state authority from acting in a law enforcement capacity within its home state or in an adjacent state if invited by that state's governor. The United States Coast Guard (under the Department of Homeland Security) is not covered by the Act either, primarily because although it is an armed service, it also has a maritime law enforcement mission."
It's confusing because DC does not have a governor so it looks like an edge case that has not been tested before.
Source: https://www.justice.gov/olc/opinion/use-national-guard-suppo...