Is there something on the NEC code that states the UFER ground needs to be permanently visible? I had my rough in electrical inspection the other day. He stated that per NEC 250.64(E) (1), I have to put an access panel in the drywall so that he is able to visibly see the UFER. I would rather not have an extra hole in my finished ceiling if not needed. Nothing I find is saying this is needed.
Wrong citation, right answer
Your inspector is right, even though their NEC citation isn't. They're after NEC 250.68(A):
(A) Accessibility. All mechanical elements used to terminate a grounding electrode conductor or bonding jumper to a grounding electrode shall be accessible.
Exception No. 1: An encased or buried connection to a concrete-encased, driven, or buried grounding electrode shall not be required to be accessible.
Exception No. 2: Exothermic or irreversible compression connections used at terminations, together with the mechanical means used to attach such terminations to fireproofed structural metal whether or not the mechanical means is reversible, shall not be required to be accessible.
So, you'll need to provide that access hatch for the "stub-up" connection from the rebar to the grounding electrode conductor, or provide some other way to access it. If the connection is irreversable, using exothermic welding or a listed compression connector, instead of being a mechanical clamp, though, then you can cover it over -- this might be worth discussing with your electrician.