Should they ignore the grammar issues and respond to the content of the question, edit without comment, edit with comment, or some other solution?
I find this is a tricky question sometimes. I personally find it very difficult to edit for spelling and grammar, and not also "improve" the question by correcting odd regional phrasing, adding commas to indicate pauses, etc. It's a fine line between "I'm fixing this so it's more readable" and "I'm fixing this to fit my standards of how things should be written".
That said, I think it's a noble thing to do in general, and it's surprisingly useful in terms of ferreting out little ambiguities. For example, when editing this question, I realized that I'd submitted the wrong answer because I confused who "he" was in the question. Editing it made that more clear to me, so I could make it more clear to others. Of course, that does raise the possibility of accidentally changing it via "correction" in much the same way that many Biblical variations came about (a scribe, coming upon a misspelled word, fixed it to the wrong word).