The Irish Moss won't change the flavor. It, and other fining agents, act by attracting the charged particles and dropping them out. The nonfermentables are sugars that the yeast can't eat, but they are in solution, so will stay put. It can cause yeast to drop out, but this is only a problem with a hefe where you want the yeast. Even if bottle conditioning, there will be enough to carbonate - may take a little longer, but longer conditioning makes it better anyway.