I once had an interview for an internship where I was asked some technical big-picture questions. I knew the answers. Got the job and was able to work on some unbelievable projects for a 20 year-old.
My GPA was good but not outstanding. For recruitment for an engineering firm, I think that in general, those with higher GPA's will perform better. Even if they are just good at cramming and test taking, it shows that they have persistence and work well under pressure.
My GPA wasn't outstanding because I was lazy when it came to classes that were not in my area of interest. However, among my structural clases I had a 4.0.
The field engineer, or any kind of engineer, who is unable to get good grades in relevant classes is likely not as prepared as the engineer who got good grades. Obviously experience can make up for the grades, but we're talking from a recruiter's perspective who is looking at applicants just out of school.
If a student really understands the material, he/she should be able to make the grade. If they cannot, then there is obviously something wrong with the test. Thankfully, that never occured in my educational experience.
That's all irrelevant though, imo, if the recruiter asks good questions. You can weed out the poor applicants in a sentence or two.