I just had one soldier with the craven and daredevil trait. Oddly enough, they acted as a daredevil and would charge at fish people.
At the moment all traits are randomly assigned and it doesn't check for anything. I think this will eventually be changed but its pretty minor right now.
...and the devs said that they are planning to introduce mental illnesses in the future... That soldier clearly has bi-polar mood swings!
yes, my daredevil and fishlover soldiers will never run from a fishman. Everyone else will flee at first sight.
Mr. Triolo is on the job of making traits affect lots of stuff, should be rolling the first round of his changes into the next patch. And I'll admit, I'm kinda in favour of contradictory traits because I want to see what happens.