Single wall rims with disc brakes
Single wall rims on disc brake wheels aren't especially any more problematic than with a rim brake. It's a pretty cynical way for bike manufacturers to allocate parts dollars, so thankfully it's not super common.
Putting a single wall rim on a cargo bike is a bad idea though. Single wall rims are far less structurally efficient than double wall, typically manifesting as being less rigid and able to support less spoke tension. (Specimens do exist that go the other direction and are strong but very heavy.) Typical singlewall aluminum ATB/hybrid rims can't really be built to more than about 70 kgf before buckling in the stand or having major fatigue problems, compared to 100 minimum for even a basic double wall. That's a massive difference in strength. Also, 25mm external is very marginal for a 60mm tire.
A Rhynolite or Rhynolite XL is an okay choice, but the world has moved on from the days when they were a great choice for something like this. They're not disc-specific, and you do get extra strength for the weight out of a proper disc-specific rim.