They are going to give up this position of relatvie comfort for religion. Almost every tigercloak follows the Red God (that's why the Triarchs wanted to hire the GC to attack the temple instead of making the tigercloaks attack their own religion) and as seen from the Volantine scenes, they are all quite fanatical in this. For them Daenerys will be AA, the saviour reborn, why on earth would they want to fight her. Another pro for giving up comfort is the Dragons. You can't enjoy higher rank when your dead. And by the way, as free men things could get even beter for them, besides fighting along side of AA gives them a-get-into-heaven-for-free-card... Don't think they'll pass on that. Also think about the fact that the Unsullied had the same choise, take revenge on those awfule slavers and be free or remaining in chains. These elite fighters chose for freedom. Personally, I think that when they see the Dragons and the queen most of them will turn to her and they'll probably fight the loyal tigercloaks. After that Dany will merge them with her own army and attack Volantis.