If you are looking for opinions mine is this:
I would wear my letters to the bar when I did not drink. If I am the DD then I am being responsible and not disgracing my letters. I don't see how the casino would be any different, if you are not drinking. For instance, if you went to a SA sister's wedding and they served alcohol would you not wear your letters if you planned on not drinking? Or if you went to a bowling alley on a date and it had a bar inside?
I believe we take some of our policies a little to literal. I would wear them if I wanted to and weren't going to drink. Just my personal opinion...nothing more