I'm not familiar with what the various companies are using to assess IQ, but Raven's progressive matrices are the most highly g-loaded of the IQ tests.
"g" is the common factor that subsumes all IQ tests, and it is g that is most predictive of job performance, salary earned, and prestige of occupation (correlations in the .5 range). G also predicts longevity and (very mildly) sperm quality, humor ability (and, in turn, reproductive success) consistent with the hypothesis that g is a biological fitness indicator.
I would think a reputable company is doing something equally as valid as Ravens, so if I were an employer, I would very much want to know what the scores of a prospective employee is.
As for personality, measurement of the Big 5 has being going on for sometime and it has been validated, but the correlations with job performance are weak (from memory, conscientiousness is the most important there).
But beyond that, you are going to spend many thousands of hours of your life with people at work. Would you, for example, want to work with someone who is neurotic, disagreeable, and who lacks conscientiousness? Not me. Again, not a strong predictive validity, more of a screen for red flags.