RE: Would the grammar police please assist!
If that's so, "He drove dangerously fast" is permissible, makes more sense, and sounds better than the others.
Driving fast is not always dangerous; driving faster than the conditions allow is.
"He drove so fast he endangered those with him." is in danger of killing the pace and sounding a little too formal. Mightr be fine in a report, not so good in fiction. "He drove dangerously fast," is cleaner, clearer, makes sense to any who read it, and is the neatest way of conveying the meaning.
Words and grammar are tools for writers to convey meaning and illicit emotions, so to my mind, breaking a rule to get a better outcome is permissible, providing it doesn't grate on the ear or bring the reader up short. And here we're back to, "Must of."