Not what they did on the surface (limiting source to only customers). That’s allowed by the GPL. But they went beyond that which imo makes them non-compliant.
RH will cancel your access/agreement if you share the GPL’d source with others. That’s directly forbidden by section 6 of the GPLv2. RH is free to cancel your agreement when they want, but not because you exercised your rights under the GPL.
Once your agreement is canceled, you also lose access to the matching source for other GPL’d packages installed on your system. RH could offer other methods to be in compliance, but as far as I know, they have not.