i just did the GC (Bespin, droid vs scoundrel) 3 time :
first time, grievious, won but my magna got nuked in the beginning, it only did his bonus turn...so no more taunt.
then did it twice with a sith empire team (malgus, DS, BF, marauder and malak), first time i won and didn't get the 5 taunt feat....second tilme i timed fear and shock application to get the most of malak unique, and even renewd malgus taunt twice....still no feat.