If Sanji hears about this tournament, I don't think he'll let Mugi or Zolo enter since there both known and will be recognized; Luffy has his straw hat and is the only rubberman whereas Zolo is infamous for his three-sword-style, he also rocks his bandanna. So the point is that Sanji will be the only one to fight in this tournament (or only one of the M3). Furthermore, if Sanji does enter solely and beats all his opponents. The Purple Tiger will definitely report to HQ that there's a SH that is near equal to Mugi and Zolo. And this will open up a window of recognition & fame for Sanji. The fame which Oda promised him.