I am not sure about each Ivy school, but there are quite a few prestigious colleges that say they actively encouage the best CC students to apply. I know Brown does, at least. Your son is going to have to accept that if he gets into an Ivy League school, there will be quite a few credits that won’t transfer over.
As far as continuing to pursue the UC transfer option, he could take a break. Stop CC classes and apply for next Fall to Ivy schools. If he doesn’t get in, he can resume CC classes, maybe apply as a spring transfer to UC.