Our kid is in dual enrollment at a local private university as a senior. The first thing you need to figure out is what is actually available; it looks like only the OSSE program (mostly community colleges, UDC, Trinity, a couple of public schools) allows students to take summer classes. So you’d need to look and see what courses are available at the list of schools that are part of that program, whether they are in-person or online, etc.
If there’s a course your kid would enjoy and you can figure out the logistics (few of the schools are in DC), I don’t see how it hurts. The expectations of the private university program, which my kid is enrolled in, are that the student manages everything themself, like a college student. I assume it’s similar for the OSSE program. So make sure your kid is ready, maturity-wise, for that experience.
Logistically, again in the private university program, it’s relatively easy. The most challenging part is getting enrolled for classes, as HS students get last dibs and often aren’t registered until the day before classes start (that may vary by university). So planning around other summer activities might be challenging. But once they’re enrolled, it’s pretty straightforward.
More info here:
https://dcps.dc.gov/service/participate-dual-enrollment