For now, nicknames are not available for the bracket diagrams. I have some folks who are certified with USBC by actual first name, but only use their nicknames. So, for now, I will be changing first names to nicknames after I print the certification cards.
The drawback will be resetting the names if they qualify for an award.
Update: I have changed the first names of my bracket players to nicknames where necessary. I'm not going to worry about resetting names for awards since they only go to the local association..