Currently there is no way to distinguish between normal and moderator only tags.
1 Answer
The tags methods now return restricted_to
and fulfills_required
(I know you didn't ask for the second one, but it was also missing).
restricted_to
will be set to a "minimum" user type if appropriate, and fulfills_required
will be set to true if it is one of the tags of which at least one must appear on a question.