Assuming you're planning to attend an NDCA sanctioned event, there are now very specific rules regarding material allowed in each level. I found a copy of the syllabus, rules and restrictions here: http://www.wright-house.com/dance/ndca-american-smooth-syllabus-ballroom-dance.html.

With respect to the Twinkle, the language appears to be deliberately vague. On the allowed list is "Simple Twinkle", which typically refers to a Twinkle of the non-brushing variety. However, further inspection contradicts that theory. On the list of things not permitted: Continuity endings, Open Naturals, and Open Reverses. Other than that, no mention is made of normal promenade Twinkles. In fact, the only reference at all to anything Twinkle-related on the not-permitted list is the rule that says Progressive Twinkles must finish by the end of the 6th measure with feet closed. Seems to me that means you can dance 5 Progressive Twinkles of the brushing variety before you are required to close your feet. And since they didn't specificaly say "No Brush Twinkles" or "All promenade Twinkles must have feet closed", you're probably allowed to dance a Brush Twinkle.

The Arthur Murray schools are the big proponents of Brush Twinkles in bronze. They are more or less flying solo on this one, as both Fred Astaire and independent teachers (myself included) think it's a bad idea. (Ever try to lead an Arthur Murray student through a closed Twinkle? They can't follow it!) Still, from what I understand, Arthur Murray has at least a few seats on the NDCA board, so no doubt the rules were created to accommodate their syllabus in addition to everybody else's. This tells me that in all likelihood, they're specifically leaving the language vague to allow for brush Twinkles, while ruling out most other continuity style actions.

Regards,
Jonathan