I think if he really wants to go to Davis, he should use the CC route.
My dd is a senior at Davis and since she’s been there, a number of her friends have switched out of the engineering majors because of the level of difficulty and their dwindling GPAs. I’m sure the College of Engineering is aware of the numbers. I agree with @ucbalumnus and think they are really looking largely at stronger GPA’s for admission into the STEM majors.
At this place and time, I don’t think contacting admissions will change your son’s admissions status unless there was new information that was missed on his initial application, as per @Gumbymom 's post.
I think that a number of students, recently, are making the mistake of considering the UCs as “safeties”. The sheer numbers of applications with more than qualified students is making it tough. Davis has become a “decent” alternate for many students who would like to get into the top tiers or similar schools. Their School of Medicine is a hope for many Bio majors.