Last month, we ate at NASCAR and used the 1/2 price certificates
(2 - $25 ones, we were able to use both on one bill).
The server also took our Annual Pass, so we got the 15% discount in addition to using the certificate.
We asked at Pastamore the next day (same Kids Eat Free deal as Pat O'Brien's) about combining that deal with the certificate, but they said no.
So, you can still use the 15% Passholder discount with your 1/2 price certificate, but not the "Kids Eat Free" deal.
Still a great deal ... Enjoy!