Basically yes. I think that when nothing is marked - the answer gets handled by a "pre filter" in such a manner that AnswerHints does not receive it for processing. I did not look into it deeply enough to be certain.
WeBWorK Main Forum
Checkboxes with partial marks
This forum has a limit to the number of forum postings you can make in a given time period - this is currently set at 10 posting(s) in 1 day