Rihanna definitely didn´t bring attention to the show. It´s just like when her albums drop, no anticipation whatsoever. The semi success only comes in the "long run" after pushing and pushing and releasing 7 different singles ready to be played on radio. She´s nothing without that.

Anyway, it is hard to tell when someone DOES bring attention to an award show and when the ratings increase by it. The only obvious example that comes to mind from the last years are the grammys ceremony from 2012, when ratings were the highest in years because Whitney mutherpucking Houston had just died and because it was Adele´s year (a true sales phenomenon we hadn´t seen in 15 years).