This may be well suited for fresh grads, but not for mid-career senior engineers.
You should seek good candidates as is. But, you already assume that one needs to prepare...
I recommend that people prepare because I've seen many many obviously smart people not make it through. It's like showing up for a singing audition without warming up your voice. You might have a beautiful voice, but you have to show it in the best condition possible.
An interview needs a greatest common denominator. That is what an undergraduate CS test is.