| Drywall screws are for supporting drywall. (Emphasis on the period)
The NEC does not address specific supporting methods, other that stating "fasten securely in place" and use products "listed" for the application.
Have drywall screws been used to support electrical equipment?
More than you can imagine.
A good inspector will catch these being used and ask for proper screws to be used. Corrosion resistant wood screws for outdoor installations, for example.
Hopefully an inspector will tell you what not to use before you use something, but not always. It is up to an installer to be knowledgeable of what is proper to use before installing the wrong produt and have to change it later. | 
Linear Mode
