Traits don't have much impact on the job, really. Sure its nice with Genious and Active for the skills, but the only trait I always pick no matter the sim, is Observant. Sure its a reward trait but it only costs 500 points, so its quite affordable (and I give it to EVERY sim I ever play). I find it very useful for my sims work collegues (especially combined with Incredibly Friendly). Means insta-friends and no tedious figuring out what traits they have.
For suspects/witnesses, I use the Show/Search SimInfo mod to find out what traits they have. I really don't want my sims to have to introduce him/herself to everyone they meet on the job.